Recently some studies have found that learning second language can lead to increase in o

问题补充：

Recently some studies have found that learning second language can lead to increase in one’s brain power.

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

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