A bone marrow test, (what) (involves) extracting fluid from the marrow, (maybe) necessary (for diagnosing) leukemia.
A、
what
B、
involves
C、
maybe
D、
for diagnosing
【正确答案】
A
【答案解析】
what不引导定语从句。引导非限制性定语从句应用which。改“what”为“which”。
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