被动语态：把收到动作的事物放前面
说明东西被制作、被使用或被送达，改变句子的关注点。
内容更新：
进入本课练习 →这一课学什么
- be + 过去分词，让动作接受者成为主语
- 过去发生的被动，用 was / were + 过去分词
be + 过去分词，让动作接受者成为主语
The team makes the posters 关注团队；The posters are made by the team 关注海报。be 根据时间和主语变化，过去分词保留。不是每个动词都能这样转换，本课选有动作对象的动词。
The room is cleaned every day.
这个房间每天都被打扫。
These bags are made in China.
这些包在中国制造。
过去发生的被动，用 was / were + 过去分词
The parcel was delivered yesterday 说明包裹昨天送达。动作执行者不重要或不知道时，可以省略 by 后的人；不要为了有被动结构而硬加 by someone。
The tickets were checked at the gate.
票在入口处被检查了。
The parcel was delivered this morning.
包裹今天上午送到了。