题目内容
Despite much research, there are still certain elements in the life cycle of the insect that _______ not fully understood.
A. are B. were C. is D. was
A
这里由引导的定语从句修饰复数名词elements,所以定语从句中的that代替的复数意义的名词,其谓语应该用复数形式;这里谈到的是现实存在的事实,排除B项。
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