【单选题】When a drug is one that should be used only under a doctor's supervision, the law requires that it be sold only by prescription (处方). Special tests or instructions may be needed. Drugs for serious dis...
A.
Because they are not safe.
B.
Because they need further special tests.
C.
Because they are meant to cure serious diseases.
D.
Because the prescription can ensure the safe use of the drugs.