My friend John insisted that he had seen alien the day before.A. aB. anC. someD. any

问题补充：

My friend John insisted that he had seen alien the day before.

A. a

B. an

C. some

D. any

答案：

A. a

(答案→)B. an

C. some

D. any

解析：本题的含义是我的朋友约翰坚持说以前他看见过外星人，修饰可数名词单数通常用不定冠词a或an，元音音素前用an，alien的第一个音为元音，故本题选B。