他以为我生气了，其实我只是太累了不想说话。

Tā yǐwéi wǒ shēngqì le, qíshí wǒ zhǐshì tài lèi le bù xiǎng shuōhuà.

He thought I was angry, but actually I was just too tired to talk.

我们都以为考试取消了，后来老师说只是推迟了一周。

Wǒmen dōu yǐwéi kǎoshì qǔxiāo le, hòulái lǎoshī shuō zhǐshì tuīchí le yì zhōu.

We all thought the exam was canceled, but later the teacher said it was just postponed by a week.

她以为男朋友忘了她的生日，没想到他准备了一个惊喜派对。

Tā yǐwéi nán péngyou wàng le tā de shēngrì, méi xiǎngdào tā zhǔnbèi le yí ge jīngxǐ pàiduì.

She thought her boyfriend had forgotten her birthday, but she didn't expect him to have prepared a surprise party.