问题描述：
帮我解释一下,这个语法时态,以及用法
There have been a number of robberies and muggings.其中,为什么用there have been,不直接用there are
There have been a number of robberies and muggings.其中,为什么用there have been,不直接用there are
问题解答：
我来补答展开全文阅读