English is useful language so that most people speak it as second language.A. a; theB. a

问题补充：

English is useful language so that most people speak it as second language.

A. a; the

B. an; the

C. an; a

D. a; a

答案：

A. a; the

B. an; the

C. an; a

(答案→)D. a; a

解析：英语中以元音音素发音开头的单数可数名词，要用不定冠词an。useful为辅音音素发音，故填a; a second 是又一个，再一个的意思. a second language第二语言.句意：英语是一门很有用的语言，所以很多人将它作为第二语言。