All your books must __________(放好) after a day's study.

All your books must __________(放好) after a day's study.
All your books must __________(放好) after a day's study.

All your books must __________(放好) after a day's study.
be put away

must be put away 书被放好是被动语态 must be done put away收好，放好 put过去分词还是put