OG Verbal 分册 2th -- 92题

三零年代

Schistosomiasis, a disease cused by a prasitic worm, is prevalent in hot, humid climates, and it has become more widespread as irrigation projects have enlarged the habitat of the freshwater snails that are the parasite's hosts for part of its life cycle.

A)  the freshwater snails that are the parasite's hosts for part of its life cycle
B)  the freshwater snails that are the parasite's hosts in part of its life cycle

OG的解释是，表示和宿主(host) 混合/融合 的一个持续时间，用介词for而不用in
可是我还是看不出来，到底for和 in都有哪些区别，还是说着就是约定俗成。

三零年代

自己顶一下

三零年代

再顶

绿小一

同问，划线部分的its 是指谁啊