Barack Obama African America was elected as 56th President of the United states.A. / the

问题补充：

Barack Obama, African America, was elected as 56th President of the United states.

A. /，the

B. /， /

C. an ， the

D. an ， /

答案：

A. /，the

B. /， /

(答案→)C. an ， the

D. an ， /

解析：前文一个美国黑人是泛指，且词首音素为元音，用不定冠词an，下文第56届美国总统是特指，用定冠词the，选C。