Pumasneverattackahumanbeingexcept()cornered?这新概念的老问题哈,可是好像谁都没说清楚.
A.theyare
B.being
C.thattheyare
D.whentheyare.except加That从句和when从句这个选项中有什么区别哈,为什么一定要选D哈?