all that can be eaten___eaten up答案是has been all为什么后面是单数?

all that can be eaten___eaten up答案是has been all为什么后面是单数? all that can be done has been done 为什么要用has,不用have all that can be eaten had been eaten up. all that can be done has been done Has all that can be done been done? all that can be done has been done. All that must be done ____(do).答案是have been done,为什么是这个答案?这句 all that can be done been done. All that can be eaten( )eaten up all that can be eaten_____eaten up all that can be done has been done.中的that为 All that can be eaten _______ eaten up. A are being B has be