— Why don’t you stay a little longer？

— ______, but I really should be on my way.

A．I wish I could

B．That’s too bad

C．Forget about it

D．It is my pleasure

明涵是指( )。

A．洞顶填土不大于50cm

B．洞顶不填土

C．洞顶填土深度小于1m

D．洞体为箱形