He is __________ unusual inventor and he invented _____

试题详情及答案解析: He is __________ unusual inventor and he invented _________ useful invention.
A. a; an B. a; a C. an; an D, an; a; 答案：D; 试题分析：句意：他是一个不寻常的发明家，而且他发明了一个有用的东西。不定冠词An用于以元音音素开头的单词前面；不定冠词A表示泛指，定冠词the用于表示特指。故选D。
考点：考查不定冠词。