关于主谓一致的单复数问题this one must have been in the possession of a private collector and somehow managed to escape.为什么用Have been 不用 Has been 不是单数么
问题描述：
关于主谓一致的单复数问题
this one must have been in the possession of a private collector and somehow managed to escape.
为什么用Have been 不用 Has been 不是单数么
答