a punctuation mark (?) placed at the end of a sentence to indicate a question
双语例句
His identity is still a question mark to most of us. 我们大多数人都不知道他的身份。
A notation, usually a question mark, calling attention to an item in order to question its validity or accuracy. 疑问号一个记号,通常为问号,以引起对某一事物的注意以便就其有效性或准确性提出质疑