I believe what they were looking for is the "accesskey" attribute. To use, press Alt + (the letter specified by accesskey).
<label for="myInput" accesskey="r"/>
<a href="https://www.w3schools.com/html/" accesskey="h">HTML</a>*
Note: Test the Alt+(letter of your choosing) before specifying it in your page to make sure that it doesn't already do something (i.e. Alt+F will usually activate the Chrome's main menu, so choose your letters wisely) Also, to make it more user-friendly, its best to indicate what letter you are using as the shortcut by underlining the letter. (i.e. as in the previous example the link should look like:
<a href="#" accesskey="h" title="Press [Alt+H] to follow link"><u>H</u>TML</a>