单选题 Don't set him {{U}}to{{/U}} talking philosophy or he'll go on all evening.
【正确答案】 A
【答案解析】[分析] 习惯搭配。 set off出发，燃放，使……开动，使(某人)开始做某事；如：Whatever you say will set her off crying．不管你说什么都会使她哭泣。set on攻击，教唆；因此选项A为答案。