OG4 阅读 Q27

Choice A is the best answer. Lines 42-44("It acts... bloodstream.") explain that ATryn "acts as a molecular bouncer, sidling up to clot-forming compounds and escorting them out of the bloodstream." Antithrombin can thus be seen as an agent that reduces the amount of dangerous clots in the bloodstream.
Choices B, C, and D are incorrect because the passage does not suggest that antithrombin stems from a rare genetic mutation, is a sequence of DNA, or occurs naturally in goats' mammary glands.