Expressing "within (it/them)" with "qizhong"
In classical Chinese, 其 means 那个, 那, or 那些, and refers to people or things previously mentioned in the sentence. It stands to reason therefore, that 其中 (qízhōng）means "among the aforementioned" or 那里面, and denotes that something belongs to, is or is part of a bigger group. This is a little like "of which" in English, where you can say, "I have 3 ties, of which 2 are silk."
Category / Group / Context + 其中
- 我 有 四辆 汽车，其中 三 辆 都 是 宝马。I have four cars. Of them, three are BMW's.
- 到处 都 有 孤独 的 人，我 只 是 其中 一 个。There are solitary people all over the place. I am just one of them.
- 人类 21 世纪 面临 许多 问题，其中 最 严重 的 是 环境 问题。Mankind faces many challenges in the 21st century. Among them, the most serious is the problem of protecting the environment.
- 工作 虽然 有时 枯燥，但是 我 乐在 其中。Although work is sometimes boring, I am able to find joy in it.
In the last example sentence, 乐在其中 means "to find pleasure in" or maybe "there is joy involved with." This sounds awkward in English, but 其中 is often used in this abstract way.