has been done
All that can be done has been done　所有能做的都做了 ,根据题意是需要过去完成时,所以答案是has been done答案是have been done.是has been done，打字错了，是现在完成时 我就不明白你怎么就会说答案是have been done.，很明显是错的啦。All that can be done是一个整体，只能是单数，这里只能是has been done