Link button doesn't validate

I have created a link button and it doesn't validate. I don't know why? I have searched for tips and everyone says it should work but it keeps showing the error?

<a href="home.html"><button id="english">English</button></a>

Image of validation errors

How many English words
do you know?
Test your English vocabulary size, and measure
how many words do you know
Online Test
Powered by Examplum