Tā de Hànyǔ shuō de fēicháng liúlì ，suǒyǐ wǒ rènwéi tā shì Zhōngguó rén.
He speaks very good Chinese so I think he must be a Chinese.
Nǐ shuō cuò le ，tā shì Yīngguó rén 。Yīnwèi tā lái Zhōngguó yǐjīng shí nián le ，suǒyǐ Hànyǔ shuō de fēicháng hǎo 。
You are wrong. He is an English man. But he has stayed in China for 10 years, so he speaks very good Chinese.
Cóng dì yī cì jiànmiàn ，wǒ jiù yǐwéi tā shì Zhōngguó rén 。
At the first sight, I thought he would be a Chinese.
以为: I think “他是中国人”, but I was wrong so we can say “我以为他是中国人”, which shows that what I thought was wrong.
认为: I think “他是中国人” and I was right so we can say “我认为他是中国人”, which shows what I thought was right. “认为” is used to express an opinion or some judgment after careful consideration.
Nǐ jīntiān zěnme méi dài sǎn ？
Why don’t you take an umbrella?
Wǒ yǐwéi jīntiān bú huì xiàyǔ 。
I thought it would not rain.
Nà míngtiān de tiānqì ne ？
What about tomorrow’s weather?
Wǒ rènwéi míngtiān yídìng shì qíngtiān 。
I think it must be a sunny day tomorrow.
Nǐ jīntiān zěnme chídào le ？
Wǒ ______jīntiān shì xīngqītiān 。
Nǐ _______tā shìhé zhè fèn gōngzuò ma ？
Wǒ _______tā bú tài shìhé zhè fèn gōngzuò 。
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