He ___ without saying good-bye to them, for he always has good manners.

A．mustn’t have left

B．may not have left

C．shouldn’t have left

D．can’t have left

（）的主要特点是多声部、无指挥、无伴奏，模拟鸟叫虫鸣、高山流水等自然之音，是一种和谐之声。

A.白族调

B.土家风俗歌

C.侗族大歌

D.回族花儿