题目
__________life could be found on Mars was once believed by scientists.A. WhatB. AsC. ThatD. While
__________life could be found on Mars was once believed by scientists.
A. What
B. As
C. That
D. While
题目解答
答案
C. That
解析
步骤 1：分析句子结构
句子的主干是“__________life could be found on Mars was once believed by scientists.”，其中“__________life could be found on Mars”是主语从句，而“was once believed by scientists”是主句。
步骤 2：确定主语从句的引导词
主语从句“__________life could be found on Mars”中，从句不缺少任何成分，因此需要一个不担任任何成分的引导词。在选项中，只有“that”可以作为不担任任何成分的引导词。
步骤 3：验证选项
将“that”代入句子中，句子变为“That life could be found on Mars was once believed by scientists.”，句子语法正确，意思完整。
句子的主干是“__________life could be found on Mars was once believed by scientists.”，其中“__________life could be found on Mars”是主语从句，而“was once believed by scientists”是主句。
步骤 2：确定主语从句的引导词
主语从句“__________life could be found on Mars”中，从句不缺少任何成分，因此需要一个不担任任何成分的引导词。在选项中，只有“that”可以作为不担任任何成分的引导词。
步骤 3：验证选项
将“that”代入句子中，句子变为“That life could be found on Mars was once believed by scientists.”，句子语法正确，意思完整。