请教SC问题,q求大牛解答Schistosomiasis, a disease caused by a parasiti

请教SC问题,q求大牛解答
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 cycleB. the freshwater snails that are the parasite's hosts in part of their life cycle C. freshwater snails which becomes the parasite's hosts for part of its life cyclesD. freshwater snails which become the hosts of the parasite during the parasite's life cyclesE. parasite's hosts, freshwater snails which become their hosts during their life cycles问题：题目中的红色的it代表的应该是parasitic worm吧？如果是这样的话，这个指代会不会引起歧义，会不会让别人理解成schistosomiasis？如果这里不是指代parasitic worm的话，我很难理解题目中的for part of its life cycle.另外，答案说B中的in part of their life cycle中的In使用的不正确，想问问大家为什么不正确？谢谢！