将主动句改为被动句的三种语态例句如下：
一般现在时的被动句
主动句：They are playing football in the park.
被动句：Football is being played in the park by them.
一般过去时的被动句
主动句：She wrote a letter to her friend.
被动句：A letter was written to her friend by her.
将来时的被动句
主动句：They will build a new house next year.
被动句：A new house will be built next year by them.
希望这些例句能帮助你更好地理解如何将主动句改为被动句。
