be to be done可以改成must be done

be to be done可以改成must be done all ( ) can be done must be done. something must be done must have been done/must be done To be done being done have done/to be done Justice must not only be done,but must be seen to be done 新概念英语2级问题用must be done,can be done,should be done,have to be What should ____ must ____.A do,do B be done,be done C to be TO BE DONE怎么样 what to be done seem to be done