an only child

独生子女

She’s the only person for the job.

她是这项工作的最佳人选。

Don’t be defending. I was only joking.

别紧张，我只是在开玩笑。

When speaking English, you should think about the message and don’t focus on the grammar rules only.

讲英语时，要考虑你要表达的意思，而不是只关注语法规则。