问题
选择题
____is certain is ___prevention is more important than treatment .
A．It;that
B．What;that
C．As;what
D．What;what
答案
答案：B
“____is certain”在句中做主语,主语从句缺少一个主语,需要用What; “___prevention is more important than treatment .”系表语从句,句意与结构完整,只有that,可以这样用