The magician picked some persons from the audience and asked them to help him with the performance．
A. by accident
B. in vain
C. at random
D. on average
网友回答
A. by accident
B. in vain
(答案→)C. at random
D. on average
解析：短语辨析。A偶然；B徒劳；C胡乱；D平均；句意：那位魔术师从何观众中胡乱调出了几个人，并请求他们帮助表演。根据句意说明C正确。