单选题 Don''t set him to talking philosophy or he''ll go on all evening.
【正确答案】 A
【答案解析】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。