情态动词被动语态的例句如下：

We should plant many trees on the mountains.

Many trees should be planted on the mountains.

Teenagers should be allowed to go out with their friends.

The book can't be found.

The flowers should be watered every day.

Cars mustn't be parked here.

The letter was written by Tom.

The package may be delivered tomorrow.

The letter must have been lost in the mail.

The documents may be lost.

This job can be done by him.

That problem should be carefully considered.

We must be told the truth.

Your teeth must be brushed.

The no-shows have to be considered when deciding the rate of overbooking.

这些例句展示了情态动词在被动语态中的使用，强调了行为的承受者并表达了说话人的态度或意愿。