PT 7 S4 Q18

In clinical trials of new medicines, half of the subjects receive the drug ... ...

Which one of the following, if true, most appropriately completes the explanation?
(A) often the subjects who receive the drug being tested develop symptoms that the experimenters recognize as side effects of the physiologically active drug
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Practice Set: "Drawing Conclusions" Questions, Set 3 - "Completes the Argument" Subset