六级练习2015.03.14
[audio]http://sound.yywz123.com/tingbbs/cet6/cet620150314.mp3[/audio]In order for a chemical to be considered a drug, it must have the capacity to affect how the body works. (1)_________________________. 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 (2)______________________. Many people suffer ill effects from drugs called side effects, (3)________________________. The human population contains a great variety of genetic variation, but drugs are tested on just a few thousand people.
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