Passage Three
In order for a chemical to be considered a drug, it must have the capacity to affect how the body works. No substance that has the power to do this is completely safe. [33]Drugs are approved only after tests have demonstrated that they are relatively safe when used as directed and when their benefits outweigh their risks. Thus some very dangerous drugs are approved because they are necessary to treat serious illnesses. Many people suffer ill-effects from drugs called side-effects even though they take the drugs exactly as directed. [34]The human population contains a great variety of genetic variation. But drugs are tested on just a few thousand people. When a particular drug is taken by millions, some people may not respond in a predictable way even though the drug has been tested. [35]A patient may also acquire a tolerance for a certain drug, which means the patient has to take ever-larger doses to produce the desired effects. Tolerance may lead to heavy situation, in which a person becomes so dependent on the drug that he or she becomes addicted to it. Addiction causes severe psychological and physical disturbances when a drug is taken away. Finally, drugs often have unwanted side-effects. They usually cause only minor discomfort, such as a skin rash, headache or sleepiness. Certain drugs, however, can produce serious adversary actions.

Questions 33 to 35 are based on the passage you have just heard.
33. Under what circumstances are drugs approved?
正確答案：D
解析：短文聽力常常是“聽到什么選什么”。錄音提到，藥物只能在經過安全測試后，并在指導下使用。故答案為B。
34. Why do many people suffer side-effects from a drug even though they take it as directed?
正確答案：C
解析：錄音提到，人們按規(guī)定服藥后會出現副作用，接著解釋，人類包含了很多遺傳變異，但是藥物測試只在部分人中間進行。由此可以概括出C。
35. What will happen when patients acquire a tolerance for a certain drug?
正確答案：A
解析：錄音提到，病人也可能會對某種藥產生抗藥性，這就意味著病人要加大劑量，以達到預期的藥效。由此可知答案為A。