It's a table .(改复数句）

They're tables.

They are tables
改复数句是将句子所有能变复数单数词变复数。

主语的复数
I——we you——you He/She/It——They
指示代词复数
this——these that——those
以上变为复数的单词是最基本的，你最好记下来
a/an+可数名词单数 （变为） 可数名词复数

例子
This is a pen.
These are pens

原句：It's a table=It is a table
It is复数：They are
table复数：tables
复数形式要把a去掉
所以：
They are tables

They are tables.

They're tables.

They are tables.