问号的英文：
question mark
unknown factor
unsolved problem
interrogation

参考例句：

Put a query against that.
在那儿加一个问号。

Put a question mark at the end of the sentence.
句末写上问号。

You have forgotten to put a query at the end of the sentence.
你忘了在句尾加个问号。

He queried my use of the word "kind".
他在我用【仁慈的】这个字打上问号。

Mr. Gilgan's face was an aggrieved question mark
吉耳干先生的面孔形成了一个受委屈的问号。

A sea cucumber, startled by the alvin, forms a question mark as it hurries away
一条海参被“阿尔文号”吓了一跳，在慌忙逃跑时卷曲成一个“问号”。

question是什么意思：
n. 问题；疑问；难题；询问；审问；疑问句
v. 询问；怀疑；探究

This is a relevant question.
这是一个中肯的问题。

It was a gift of a question.
解答那一道题不费吹灰之力。

This is a multiple question.
这是个复杂的问题。

mark是什么意思：
n. 符号；记号；分数，成绩；污点；迹象
v. 做记号；做标记；表明方位；标志；庆祝

Marking: Every package shall be marked with “SM” in diamond and marked the package number.
麦头每件包装应刷上菱形图案内有二字,并应刷上件号

impress a mark on [ upon ] a surface=impress a surface with a mark
在表面上打记号

To mark or mottle with spots.
有斑点，成斑驳用点作标记或使斑驳杂色

unknown是什么意思：
adj. 未知的；不出名的；陌生的；从不存在的
n. 未知的事物；默默无闻的人；未知数