all that can be eaten_____eaten up

all that can be eaten_____eaten up 一个题 英语语法All that can be eaten_____eaten up.A.have beenB.has All that can be eaten( )eaten up all that can be eaten had been eaten up. 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. A are being B has be All that can be done___________ all that can be done been done. All that can be done _______(be)done 美国陆军征募标语be all that you can be是什么意思 all that can be done has been done Has all that can be done been done?