---- How about the party ______ in Tom’s house last night ?

---- I don’t know. I was too busy to attend it.

A．held

B．to hold

C．being held

D．to be held

对树中的一个节点x，在先根序列中的序号为pre(x)，在后根序列中的序号为post(z)，若树中节点x是节点y的祖先，则下列4个序列中，（）是正确的。

A.pre(x)＞pre(y)和post(x)＞post(y)

B. pre(x)＞pre(y)和post(x)＜post(y)

C.pre(x)＜pre(y)和post(x)＞post(y)

D.pre(x)＜pre(y)和post(x)＜post(y)