所以提高了nitrates就能够抵抗病毒入侵
This is a stretch. Nowhere in the passage says that macrophage "can easily fightoff most types of bacterial infections." So B is wrong.
-- by 会员 sdcar2010 (2011/11/26 10:49:15)
"play a role" is a much softer modifier which could enhance or inhibit.
Granted, GWD questions are not authentic GMAT question. So some not well-crafted questions like this are common.
-- by 会员 sdcar2010 (2011/11/26 12:23:51)