—Believe me all your efforts will some day.—Thanks for your encouragement.A. pay backB. p

问题补充：

—Believe me，all your efforts will some day.

—Thanks for your encouragement.

A. pay back

B. pay down

C. pay off

D. pay for

答案：

A. pay back

B. pay down

(答案→)C. pay off

D. pay for

解析：句意：相信我，你所有的努力总有一天会有回报的。pay back“偿还”；pay down“即时支付，付定金；(分期付款等)付额款”；pay off“付清；偿清；有回报”；pay for“为……付款”。由句意可知，C项符合题意。