To his parents’ great joy all their son’s years of hard work finally .A. set offB. paid o

问题补充：

To his parents’ great joy, all their son’s years of hard work finally .

A. set off

B. paid off

C. took off

D. got off

答案：

A. set off

(答案→)B. paid off

C. took off

D. got off

解析：考察词组。Set off 引爆 pay off取得回报 take off 起飞，腾飞 get off下车

句意为，令他父母感到高兴的是，他们儿子这么多年的努力终于取得了回报。