問題詳情

<B> Scientists are conducting experiments to learn the causes of tooth decay, how it develops, and how to stop it.What causes tooth decay? Bacteria called “S. mutans” is the main cause. S. mutans produces a substance that breaksdown sugars into lactic acid. Lactic acid can eat away tooth enamel, which is the outer covering of the teeth. Since S. mutans gives our teeth so much trouble, a vaccine to protect against S. mutans could stop most toothdecay before it starts. Such a vaccine has been developed. Scientists injected certain rats, hamsters, and monkeyswith S. mutans cells. Other animals in the test got no injections. Then, all the animals were fed food that contained alot of sugar. The animals that received the injections had fewer cavities than the group that had no injections. The vaccine seems to work on animals. But does it work on humans? And is it safe? Even if the vaccine seemssafe now, could there be problems later for the people who got S. mutans shots? Should a vaccine that preventstooth decay be used at all time? Since tooth decay does not threaten life, some scientists question the value andsafety of using a vaccine to prevent it.                                                                   (From Project Achievement: Reading Book E)
53. S. mutans is __________.
(A) a form of tooth decay
(B) a substance containing lactic acid
(C) a kind of bacteria in the mouth
(D) a kind of medicine

參考答案

答案：C[無官方正解]
難度：適中0.571429
統計：A(1),B(2),C(4),D(0),E(0)

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