This is from question #92 in the Verbal Review 2nd Edition:

Schistosomiasis, a disease caused by a parasitic 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 their life cycle

(c) freshwater snails which become the parasite's hosts for part of its life cycles

(d) freshwater snails which become the hosts of the parasite during the parasite's life cycle

(e) parasite's hosts, freshwater snails which become their hostsduring their life cycles

Basically, I am confused about the pronouns in this question. "it" refers to schistosomiasis in the non-underlined portion of the sentence, yet "it" also refers to "the parasite" in the correct answer choice (A).

Is it possible to have a pronoun refer to 2 different nouns in a sentence on the GMAT?

Also, "the parasite" is never mentioned in the sentence. Instead, "the parasite's hosts" are mentioned in the sentence, so I assumed that the pronoun "its" did not have a clear antecedent. Please tell me why I am wrong.