He tried to invite some famous pop stars to sing in the concert , but failed.
A. with free
B. for freely
C. with freedom
D. for free
网友回答
A. with free
B. for freely
C. with freedom
(答案→)D. for free
解析：考查词组：for free免费，句意：他想邀请一些著名的流行歌星在音乐会免费唱歌，但失败了。选D。