The blues has been _____part of African-American culture since then, and it is still ______ important part of American culture.

A．a; a

B．/ ; an

C．the ; a

D．/ ; a

在使用门口送客礼时，最好让客人（）再返回自己的工作岗位。

A、出门后

B、转身后

C、上车后

D、离开视线范围以外