I can appreciate the incorrect answer choice (C), and have a follow up question to why it is incorrect:
"When the soundness of a strategy depends on the truth of a certain assumption, the first step in putting the strategy into effect must be to test the truth of this assumption."
I like this idea, they can only effectively treat a certain disease, and success of that requires the patient to have that particular disease. I think the next part fits, as well, except for the word must, if the test makers used the word would, would that alter the impact on the stimulus, and if so, in what way. I believe they both imply certainty, with one ascribing to the present moment, and the other a moment sometime after the present moment.