When it research into heart disease and its effects on the body, we do not have adequate substitutes for the use of animals.
A. refers to
B. related to
C. es to
D. talks to
网友回答
A. refers to
B. related to
(答案→)C. es to
D. talks to
解析：考查句型：when it es to 当谈到什么的时候，当谈到研究心脏病以及心脏病对人体影响的时候，我们没有足够的替代品在动物身上使用。故选C。