— I visited the Purple Mountain Observatory last Sunday.

—______ Why didn’t you tell me earlier?

A．You did?

B．I hope so.

C．Have a good time!

D．It’s so kind of you.

我国西北地区干旱为主的自然景观的主要成因是(    )

A．地处北半球亚洲高压的范围之内

B．地处东南风的背风坡

C．深居内陆又隔崇山峻岭

D．气候干旱、植被稀少、河短水少