单选题He has a(n) _____ attitude toward his work; he likes it and does it very well.

单选题How many of those trial implants fail to survive?

单选题The word "something" in the following choiceＡ),"things" inＢ)andＣ), and "events" in Ｄ)have similar meaning EXCEPT______

单选题He is ______ about his chances of winning a gold medal in the Olympics next year.

单选题The last paragraph implies that ______ the importance of protecting the earth.

单选题Mr. Morton gradually ______ a knowledge of the subject.

单选题Nearly 4 out of 5 workers at the company take unpaid ______ at least once a week.

单选题 Officials at the White House announced a new space policy focused on managing the increasing number of satellites that companies and governments arc launching into space. Space Policy Directive-3 lays out general guidelines for the United States to mitigate (缓解) the effects of space debris and track and manage traffic in space. This policy sets the stage for the Department of Commerce to take over the management of traffic in space. The department will make sure that newly launched satellites don't use radio frequencies that would interfere with existing satellites, and schedule when such new satellites can be launched. This only applies to American space activities, but the hope is that it will help standardize a set of norms in the dawning commercial spaceflight industry throughout the world. Space, especially the space directly around our planet, is getting more crowded as more governments and companies launch satellites. One impetus for the policy is that companies are already starting to build massive constellations (星座), comprising hundreds or thousands of satellites with many moving parts among them. With so much stuff in space, and a limited area around our planet, the government wants to reduce the chances of a collision. Two or more satellites slamming into each other could create many more out-of-control bits that would pose even more hazards to the growing collection of satellites in space. And it's not like this hasn't happened before. In 2009 an old Russian craft slammed into a communications satellite, creating a cloud of hundreds of pieces of debris and putting other hardware at risk. Journalist Sarah Scoles reports that NASA currently tracks about 24,000 objects in space, and in 2016 the Air Force had to issue 3,995,874 warnings to satellite owners alerting them to a potential nearby threat from another satellite or bit of debris. That's why this new policy also includes directions to update the current U.S. Government Orbital Debris Mitigation Standard Practices, which already require any entity that launches a satellite or spacecraft to vigorously analyze the likelihood that any of their actions, from an unexpected failure or normal operations, will create more space debris. It includes accounting for any piece of debris they plan to release over 5mm that might stay in orbit for 25 years or more. It might seem surprising to think about an item staying in space for that long, but the oldest satellite still in orbit—Vanguard 1—turned 60 in 2018. Agencies and companies throughout the world are working on developing technology that would dispose of or capture space debris before it causes serious damage. But for now, the U.S. government is more focused on preventing new debris from forming than taking the trash out of orbit.

单选题The relationship between corpulence and disease remains controversial, although statistics clearly ______ reduced life expectancy chronic obesity.

单选题If you were to ask him ______ his money, he would have difficulty recalling it.

单选题The difference is so small as to be ______.

单选题--If you are offered a trip to the moon, ______ it?--Of course. Why not?

单选题Many people proposed that a national committee be formed to discuss______to existing mass transit systems. A.substitutes B.measures C.duplicates D.alternatives

单选题The FBI arrived in time to prevent the ______ -- of the secret documents.

单选题It is ______ he is determined.

单选题If you want to do well on the exam, you ______ on the directions that the professor gives and take exact notes.

单选题Since any answer may bring ______ to his government, the spokesman tried to avoid the question.

单选题Most people have come to realize that it is about time the government ______ further measures to control the population. A. must take B. is taking C. takes D. took

单选题Mr. White works with a chemicals import & export company, but he ______ for this industrial fair, since he is on leave. A. has worked B. works C. has been working D. is working

单选题Since the ______ of human history, human beings have been asking questions like "What is the essence of life"