While (A) correctly identifies the claim in the question stem as a conclusion, the conclusion does not follow from the premise that microorganisms are too numerous for medicines to eliminate them entirely. Rather, the problem is that microorganisms quickly evolve immunities.

(B) correctly identifies the claim in the question stem as the conclusion, and shows the correct relationship between the conclusion and the support. It is the response of microorganisms to medicines––their ability to evolve immunities––that supports the conclusion.

The claim in the question stem is the conclusion, not a premise.

The claim in the question stem is the conclusion; it is not a generalization. Further, the claim in the question stem is a claim about the existence of disease in the world, not a prediction about how microorganisms respond to medicine.

(E) does correctly identify the claim in the question stem as a conclusion. However, the problem with medicines isn’t that the microorganisms that they are designed to kill are immune to them; instead, the problem with medicines is that microorganisms respond by becoming immune.