Sentences may also be identified as topic-comment structures in the following situations:
(1) When a modal verb is present:
一个人应该学一门外语。
Yī gè rén yīng gāi xué yī mén wài yǔ。
One should learn a foreign language.
锻炼能增强人的体质。
Duàn liàn néng zēng qiáng rén de tǐ zhì。
Exercise can improve one’s physique.
(2) When the sentence particle 了 le is incorporated (see Unit 8):
孩子上学去了。
Hái zǐ shàng xué qù le。
The child has gone to school.
太阳出来了。
Tài yáng chū lái le。
The sun has come out.
(3) When a passive notion is implied (without the use of 被 bèi structure):
衣服都洗干净了。
Yī fú dōu xǐ gàn jìng le。
The clothes have all been washed.
饭煮好了。
Fàn zhǔ hǎo le。
The meal is ready. (lit. The food has been cooked.)
(4) When a verb is unmodified or unmarked for aspect and indicates a permanent characteristic:
猫吃鱼。
Cats eat fish.
Māo chī yú。
铁爱生锈。
Tiě ài shēng xiù。
Iron rusts easily. (lit. Iron is apt to rust.)
旅游增进见闻。
Lǚ yóu zēng jìn jiàn wén。
Travelling broadens knowledge.
他喜欢打篮球。
Tā xǐ huān dǎ lán qiú。
He likes playing basketball.
[1] Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.