The subject of a sentence and its verb must agree in number.

句子的主语和动词的数必须一致。

《牛津词典》

In the sentence 'They live in the country', the plural form of the verb 'live' is in agreement with the plural subject 'they'.

在They live in the country一句中，动词复数形式live与复数主语they一致。

《牛津词典》

Do you not know that every sentence has a subject, and that, if the subject were nothing, the sentence would be nonsense?

难道你不知道每一句话都有一个主语吗？那么，如果主语都不存在，句子不是就没有意义了吗？

youdao

In just 19 words, it provides an impressive selection of current widespread writing woes: dangling modifier ("vestiges" didn't walk in the front door), poor word choice ("vestiges, " "domesticity, " "regardless"), excessive prepositions (four in all) and an underappreciated but pervasive ill, a weak sentence-subject ("vestiges").

WSJ: Word Craft: Ben Yagoda on Not Writing Badly

Inside the newsroom, her schoolteacherlike way of elongating words and drawing out the last word of each sentence is a subject of endless conversation and expert mimicry.

NEWYORKER: Changing Times

In the session on article and feature writing, the lecture covered -- how to select a subject, how to write a theme sentence to determine the parameters of the subject, and how to collect and sort out the material.

UNESCO: Communication and Information