—I’m confident that we’ll win this time.—You’ve been practicing so long.A. Are you serious

问题补充：

—I’m confident that we’ll win this time.

—You’ve been practicing so long.

A. Are you serious?

B. So what?

C. I bet you can.

D. Go ahead.

答案：

A. Are you serious?

B. So what?

(答案→)C. I bet you can.

D. Go ahead.

解析：考察交际用语。A你是认真的吗？B那又怎么样？C我确信你可以；D去做吧！句意：—我相信我们这次会赢的。—我确信你们能赢。那么一直在训练了如此长的时间。根据句意说明与前面的一致，表示确认同意。故C正确。