题目内容
When ____ comes to research into heart disease and the effects on the body,we do not have adequate substitutes for the use of animals.
A. that B. it C. what D. this
B
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题目内容
When ____ comes to research into heart disease and the effects on the body,we do not have adequate substitutes for the use of animals.
A. that B. it C. what D. this
B