When es to research into heart disease and its effects on the body, we do not have adequate substitutes for the use of animals.
A. that
B. it
C. this
D. what
网友回答
A. that
(答案→)B. it
C. this
D. what
解析：考查固定句型：when it es to“当涉及…的时候”，句意是：当涉及研究心脏病和它对身体的影响时，我们不会有适当的代用品来代替动物。选B。