在 Are you kidding? means 中为什么 means 要加复数?

mean

(1)mean  vt.意思是;表示…的意思;作…解释 三人称单数需要加s

In modern Welsh, 'glas' means 'blue'.

在现代威尔士语中，glas 意为“蓝色”。

What does 'evidence' mean?  

evidence 是什么意思？

(2)means    n.方法（ mean的名词复数）; 手段; 收入; 财富;

The move is a means to fight crime.

采取这项举措是为了打击犯罪。

The army had perfected the use of terror as a means of controlling the population.

军队已经深谙利用恐怖手段控制民众之道。

He did not have the means to compensate her.  

他没有钱来补偿她。