What is the similarity among these numbers?  $64$~ ~$100$~ ~$81$~ ~$9$~ ~$144$~ ~$16$~ ~$25$ 
选项为:A:They are all even numbers.  B:All of them can be written as $n^{2}$ ($n$ is a whole number).  C:There is no similarity.  请回答其中一个选项.