单选题 A useful definition of an air pollutant is a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or material adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled—a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapour might be considered an air pollutant under certain conditions. Many of the more important air pollutants, such as sulphur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the earth developed, the concentrations of these pollutants were altered by various chemical reactions; they became components in biogeochemical cycles. These reactions serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities. However, human production usually occurs in a localized area, such as a city. In this localized region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulphur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural level of 0.1ppm and is not usually a pollutant until its level reaches about 15ppm.

单选题The response to our financial appeal______anything we expected.

单选题The {{U}}rigor{{/U}} of the winter in Russia was often described by Mogol.

单选题Since Dick was busy, he rarely had time to go to the cinema; ______.

单选题At first Jackie prayed, frozen in fear, but gradually his terror ______ curiosity.

单选题Looking back on my childhood, I am convinced that naturalists are born and not made. Although we were all brought up in the same way, my brothers and sisters soon 27 their pressed flowers and insects. Unlike them, I had no ear for music and languages. I was not an 28 reader and I could not do mental arithmetic. Before World War I we spent our summer holidays in Hungary. I have only the 29 memory of the house we lived in and of my room and my toys. But I do have a crystal-clear memory of the dogs, the farm animals, the local birds, and above all, the insects. I am a naturalist, not a scientist. I have a strong love of the natural world and my 30 had led me into varied investigations. I love discussing my 31 topics and enjoy burning the midnight oil while reading about other people's observations and 32 Then something happens that brings these observations together in my conscious mind. Suddenly you fancy you see the answer to the riddle, because it all seems to fit 33 together. This has resulted in my publishing 300 papers and books, which some might 34 with the title of scientific research. But curiosity, a keen eye, a good memory and enjoyment of the animal and plant world do not make a scientist. A scientist requires not only 35 but hard training, determination and a goal. A scientist, up to a point, can be made. A naturalist is born. If you can 36 the two, you get the best of both worlds. A. combine B. connect C. serf-discipline D. enthusiasm E. regulations F. discoveries G. dim H. eventually I. abandoned J. honor K. disposed L. modest M. favorite N. early O. perfectly

单选题Thank you for applying for a position with our firm. We do not have any openings at this time, but we shall keep your application on ______ for two months.

单选题The President______his deputy to act for him while he was abroad.

单选题The manager was very pleased with the increased ______ from the factory last month.

单选题They are seeking to ______ the most advanced technological levels in the world.

单选题Many troubles ______ from this misunderstanding.

单选题Insomnia, or “poor sleep”, can have bad effects on a persons health and general well-being. It can_____21on both our physical and mental health and can lead to other health_____22. Insomnia can b

单选题 For years, the U.S. has experienced a shortage of registered nurses. The Bureau of Labor Statistics projects that while the number of nurses will increase by 19 percent by 2022, demand will grow faster than supply, and that there will be over one million unfilled nursing jobs by then. So what's the solution? Robots. Japan is ahead of the curve when it comes to this trend. Toyohashi University of Technology has developed Terapio, a robotic medical cart that can make hospital rounds, deliver medications and other items, and retrieve records. It follows a specific individual, such as a doctor or nurse, who can use it to record and access patient data. This type of robot will likely be one of the first to be implemented in hospitals because it has fairly minimal patient contact. Robots capable of social engagement help with loneliness as well as cognitive functioning, but the robot itself doesn't have to engage directly—it can serve as an intermediary for human communication. Telepresence robots such as MantaroBot, Vgo, and Giraff can be controlled through a computer, smartphone, or tablet, allowing family members or doctors to remotely monitor patients or Skype them, often via a screen where the robot's 'face' would be. If you can't get to the nursing home to visit grandma, you can use a telepresence robot to hang out with her. A 2016 study found that users had a 'consistently positive attitude' about the Giraff robot's ability to enhance communication and decrease feelings of loneliness. A robot's appearance affects its ability to successfully interact with humans, which is why the RIKENTRI Collaboration Center for Human-Interactive Robot Research decided to develop a robotic nurse that looks like a huge teddy bear. RIBA (Robot for Interactive Body Assistance), also known as 'Robear', can help patients into and out of wheelchairs and beds with its strong arms. On the less cute and more scary side there is Actroid F, which is so human-like that some patients may not know the difference. This conversational robot companion has cameras in its eyes, which allow it to track patients and use appropriate facial expressions and body language in its interactions. During a month-long hospital trial, researchers asked 70 patients how they felt being around the robot and 'only three or four said they didn't like having it around.' It's important to note that robotic nurses don't decide courses of treatment or make diagnoses (though robot doctors and surgeons may not be far off). Instead, they perform routine and laborious tasks, freeing nurses up to attend to patients with immediate needs. This is one industry where it seems the integration of robots will lead to collaboration, not replacement.

单选题—Did you tell him where she ______? —Yes. And I also told him she ______ until the next month.

单选题Hosting the 2008 Olympics provided China with an opportunity to ______ its unprecedented progress.

单选题The representative of the committee was asked to Uverify/U his earlier statement.

单选题Her research indicates (what) many adults routinely subscribe (to) some form of what the scholar (calls) "the magical law of (contagion)".

单选题He came back later, ______ which time they had left.

单选题I have given up trying to convince him, there is no point ______ with him.

单选题______ we need to complete the construction is two million dollars. A. All what B. That all C. That D. What