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