He devoted most of his time to researching into space, believing his hard work would ______ sooner or later.
A.pay back
B.pay for
C.pay off
D.pay up
网友回答
C解析考查短语辨析，pay back偿还，pay for为了什么付款，pay off还清，得到回报，pay up 付清，句意：他把他的大部分时间献身于研究太空，相信他的努力工作迟早会得到回报的。故选C。