Such a fierce dog _____ that we had to wait outside before we could get into his yard.

A．has he had

B．did he have

C．he has

D．he has had

如果进栈序列为A，B，C，D，则可能的出栈序列是（）。

A．C，A，D，B

B．B，D，C，A

C．C，D，A，B

D．任意顺序