问题描述: They _____ having a picnic.A.don't B.aren't C.can't选哪个? 1个回答 分类:综合 2014-12-13 问题解答: 我来补答 B理由1.“they” → 要选复数形式的2.“having” → 要选be动词(be doing) 展开全文阅读