After they had arrived campus a girl was sssigned to take them on a tour of the halls
问题描述：
After they had arrived campus a girl was sssigned to take them on a tour of the halls
这个地方为什么要用 过去 完成时
答
因为这个动作是发生在girl was sssigned to take them on a tour of the halls之前的.因为girl的动作用的是过去时,过去的过去就用过去完成时.我们老师教我们,看这个动作和主语发生的动作有没有时间差、如果有时间差,...