单选题 Bacteria are microscopic organisms which live on the surface of objects. They are one of the most ancient living things, which exist on this planet for nearly 4,000 million years. Do you know the size of bacteria? It can only be measured in microns. Maybe you have not a standard in your mind how long a micron is. One micron is a thousandth of a millimeter, which equals about the diameter of a pinhead. Therefore, even if we enlarged the rounded bacterium a thousand times, it would only be the size of a pinhead. We barely see bacteria by a magnification an ordinary microscope of 100 times, even if we try, we cannot make out anything of their structure. There are normally millions of them together, for they can multiply really fast.
Scientists have found that some bacteria have attached to wavy-looking "hairs" called flagella. The flagella rotate, pushing the bacteria through the water. Others can glide along over surfaces by some little-understood mechanism. Bacteria are so small that they are influenced by the movements of the chemical molecules around them. They are active all the time. Even the bacteria without flagella often bound about in the water. They are pushed here and there, colliding with the watery molecules.
Bacteria cannot be detected because they don"t produce bad odor or change the color or texture of the food. Therefore, when people eat the food with many bacteria, they are likely to get hepatitis A, acute gastroenteritis and a host of other illnesses. Many households have refrigerators to prevent from bacteria. Of course, freezing food slows or stops the growth of bacteria, however, when food is thawed, the bacteria will become reactivated. Bacteria can not be totally destroyed before the food is thoroughly cooked. We need to know that not all bacteria are in connection with illness. Just some bacteria can cause disease. They are called pathogenic bacteria. Fortunately our immune system can protect us from them.
Bacteria are prokaryotes ( single cells that do not contain a nucleus). It may seem weird to classify organisms according to such details, but with or without a nucleus is not trivial at all. The division between prokaryotes and eukaryotes (all organisms with a nucleus inside their cells) is of extreme importance in biology, and is the result of a major evolutionary breakthrough. Visit our program tomorrow if you want to know more, thank you.

单选题 Which statement is not true about flagella?

【正确答案】 A

【答案解析】[解析] 此题考查考生对文章细节的理解能力。
根据第二段第一句中“some bacteria have attached to wavy-looking "hairs" called flagella”可见，细菌是附着在鞭毛上的，鞭毛并不是细菌内部的组成部分，A项不符合文意。根据该句中“wavy-looking hairs”可见鞭毛的外表呈波浪状，D项正确。根据第二段第二句“The flagella rotate, pushing the bacteria through the water.”可见，鞭毛可以推动细菌在水中行进，B项正确。根据该句的前半句可知，鞭毛的运动方式是旋转式的，C项正确。故正确答案为A选项。

单选题 What is the meaning of "collide" in the second paragraph?

【正确答案】 A

【答案解析】[解析] 此题考查考生对词义的推断能力。
根据第二段第四句“Bacteria are so small that they are influenced by the movements of the chemical molecules around them.”可知，细菌是如此微小，以至于周围化学分子的活动会对它们产生影响。以及本段最后一句中“They are pushed here and there…with the watery molecules.”可以推断出，细菌之所以弹往各个方向，是因为受到了水分子的“撞击”，故正确答案为A选项。

单选题 Which of the following ways can help people prevent from bacteria?

【正确答案】 C

【答案解析】[解析] 此题考查考生对细节的理解能力。
根据文章第三段第一句“Bacteria cannot be detected because they don"t produce bad odor or change the color…”可见，食物有没有细菌，只靠看或者是嗅是没有用的。A错误。根据本段第四句 “Of course, freezing food slows or stops the growth of bacteria…”可见，冰箱里的食物其实也不一定安全，因为把食品冷冻可以放慢或使细菌停止生长，但不会彻底消灭细菌。B错误。根据本段倒数第四句 “Bacteria can not be totally destroyed…before the food is thoroughly cookde”可以看出，除非食物彻底煮熟，细菌才有可能被破坏。所以C项正确。D项意为“在食物解冻之前吃”，根据常识，此项不合逻辑。故正确答案为C选项。

单选题 What can be inferred from the last paragraph?

【正确答案】 C

【答案解析】[解析] 此题考查考生对文章的推理能力。
根据最后一段第二句It may…“but with or without a nucleus is not trivial at all.”以及第三句“The division between prokaryotes and eukaryotes…is of extreme importance in biology．”可见，是否有细胞核这种区分对于生物学是很重要的，A项直接体现了文意，而小是推断出来的，故不选。根据该段倒数第二句“The division between prokaryotes…and is the result of a major evolutionary breakthrough．”可以推断出，明天的节目很可能会接着讨论进化问题，D项原文没有涉及，故正确答案为C选项。

单选题 Which of the following is true according to the first paragraph?

【正确答案】 D

【答案解析】[解析] 此题考查考生对文章细节的理解能力。
根据第一段中第四句“It can only be measured in microns.”可见，细菌只能以微米来计算，故D项正确。根据该段第六句“One micro is a thousandth of a millimeter, which equals about the diameter of a pinhead.”可见，一微米等于千分之一毫米，一毫米大约等于针头的直径，即细菌的大小相当于针头直径的千分之一，故A项错误。根据该段第八句“We barely see bacteria by…”可见，用普通的显微镜是很难看到细菌的。这句话重点在于“barely”，意为“几乎不”，故B项错误。根据该段第七句和第八句“Therefore, even if we enlarged the rounded bacterium a thousand times, it would only be the size of a pinhead. We barely see bacteria by a magnification an ordinary microscope of 100 times, even if we try, we cannot make out anything of their structure.”可知，我们看不到细菌是因为细菌太小，并不是因为它们经常簇拥在一起，C项错误，故正确答案为D选项。