Scientists are still trying hard to find out....caused SARS to spread so rapidly.A.what was it that B.what it was that C.what was D.what was that为什么不能选C
热心网友
该句可这样分析:将从句还原成独立句子B为：it was (what) caused SARS to spread so rapidly （即it is/was ... that ...的强调句式）C为：(what) was caused SARS to spread so rapidly (为病句）
热心网友
it was\is...........that.....强调句科学家试图弄清：是什么使SARS 病毒传播的如此迅速！（根据意思来看应该用主动形式）所以选B，宾语从句用陈述语序
热心网友
选c后面的从句里就缺形式主语了
热心网友
选B