Has all that can be done been done?
为什么用HAS 不用 HAVE
PEOPLE也是整体,动词用复数
先换成陈述句＝all that can be done has been done
主语＝all
定语＝that can be done
谓语＝has been done（被动）
转换成简单的主句＝all has been done
all 作为一个整体,集合名词所以用单数
我的意思是为什么用HAS 不用 HAVE
PEOPLE也是整体，动词用复数
that为主语的话，无论that指的是单数还是复数，谓语动词都要用单数？