According to a new survey carried out by an American university learning second language

问题补充：

According to a new survey carried out by an American university, learning second language can result in increase in the power to learn your native tongue.

A. a; the

B. 不填; the

C. a; an

D. the; an

答案：

A. a; the

B. 不填; the

(答案→)C. a; an

D. the; an

解析：考查冠词：第一空填a，a second language”泛指一门第二外语; 后面的increase 作名词讲, 是可数名词, 前面需加不定冠词an。句意：根据一个美国大学最近的调查，学习一门外语可以导致学习本族语能力的增加。选C。