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

某班抽取6名同学参加体能测试，成绩如下：85，95，85，80，80，85．下列表述错误的是（　　）

A．众数是85

B．平均数是85

C．中位数是80

D．极差是15