—What a nice classroom!

—It _____ every day.

A．is cleaning

B．has cleaned

C．must clean

D．is cleaned

椎-基底动脉系统短暂性脑缺血发作最常见的临床表现为（）。

A.眩晕、恶心和呕吐

B.耳鸣和耳聋

C.跌倒发作

D.吞咽困难

E.复视