249.Doctors still know little about how the Listeria bacterium is spread and why the disease it causes, listeriosis, afflicts some people in a contaminated area though it spares many others. (A) though it spares (B) where it spares (C) despite sparing (D) when sparing (E) while sparing
关于it的制代,要根据句子意思来判断的,前一个it(the disease it causes)明显指代细菌,因为只有细菌causes disease
后一个it(A,B选项里的it,though it spares)指代the disease,因为why the disease it(指代Listeria bacterium ) causes, listeriosis, afflicts some people in a contaminated area though it spares many others.句子意思表明后面的it指代the disease(listeriosis)