你为什么早退？记住，在疑问句的末尾总要使用问号。

Why did you leave early? Remember to always use a ___question ___mark at the end of a question.

她句子里的唯一错误是漏掉了一个问号。

The only mistake in her sentence was a missing ___question ___mark.

在正式写作中，问号也可以用来表达对某个事实的怀疑。

In formal writing, a ___question ___mark can also be used to express doubt about a fact.