Helen ________ her keys in the office so she had to wait until her husband ______ home.

A．has left; comes

B．left; had come

C．had left; came

D．had left; would come

非空的循环单链表head的尾结点(由p所指向)，满足( )

A．p－＞next＝＝NULI

B．p＝＝NULL

C．p-＞next=head

D．p＝head