We are going to have a barbecue _______ it rains
问题描述：
We are going to have a barbecue _______ it rains
A.if not B.when C.except that D.unless
选什么,为什么,劳烦把每一项分析一下
答
选D unless 除非
A if not意思是如果不,但是不能直接用 if not it rains,而应该是 if it does not rain
B when 当, 当下雨我们去烧烤,显然不对
C except that 是除了……,此处不适用.例句：Your homework is good except for some spelling mistakes. 你的作业不错就是有点拼写错误.