问题
选择题
It is already well understood___________ causes the global warming.
A．what
B．when
C．how
D．that
答案
答案：A
考查名词性从句。此题为it 作形式主语，真正的主语是后面的从句，从句中缺少主语，所以用what。
搜题请搜索小程序“爱下问搜题”
It is already well understood___________ causes the global warming.
A．what
B．when
C．how
D．that
答案：A
考查名词性从句。此题为it 作形式主语，真正的主语是后面的从句，从句中缺少主语，所以用what。