conjunctions:否则,不然
你得小心驾驶,否则会出事故?
Nǐ dé xiǎo xīn jià shǐ ,fǒu zé huì chū shì gù ?
You should drive carefully, or you’ll have an accident.
我年级大了,不然我会去参加游泳比赛。
Nǐ dé xiǎo xīn jià shǐ ,fǒu zé huì chū shì gù ?wǒ nián jí dà le ,bú rán wǒ huì qù cān jiā yóu yǒng bǐ sài 。
I am getting old, otherwise I would take/have taken part in the swimming competition.
[1] Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.