Choice A is the best answer. The previous question asks what the Venus flytrap gains from requiring multiple triggers before closing. The answer, that multiple triggers allow the plant to conserve energy, is best supported near the beginning of the first paragraph: "Closing its trap requires a huge expense of energy, and reopening the trap can take several hours, so Dionaea only wants to spring closed when it's sure that the dawdling insect visiting its surface is large enough to be worth its time."
Choices B, C, and D are incorrect because the cited lines don't support the answer to the previous question. Instead, they describe how the hairs on the Venus flytrap function and how the system of multiple triggers works (choices B and C) and explain how the plant preserves a memory, as it were, that something has touched the trigger hairs (choice D).