大全 371

371.        In cold-water habitats, certain invertebrates and fish convert starches into complex carbohydrates called glycerols, in effect manufacturing its own antifreeze.

(A) in effect manufacturing its own antifreeze

(B) effectively manufacturing antifreeze of its own

(C) in effect manufacturing their own antifreeze

(D) so that they manufacture their own antifreeze（C）

(E) thus the manufacture of its own antifreeze

单复数排除ABE，但是C为什么优于D，D也没有语法错误

而且they指代不明确