【题目】The magician picked several persons ______ from the audience and asked them to help him with the performance.
A. by accident B. at random C. at risk D. on average
在线课程【答案】B
【解析】
试题分析：考查介词短语辨析。介词短语by accident偶然；at random胡乱；at risk冒险；on average平均；句意：魔术师从观众中胡乱挑选了几个人，请他们帮助他进行表演。根据句意可知B正确。