Hello good, I write because since I copied the code of the drop-down menu (navbar) that came in the example and pressing the dropdownList should work, but it does not work and I don't know what to do, it is the first time that I am occupying this material, since I found that I had cool stuff

I must clarify that I made the references mentioned in the page and nothing.

https://mdbootstrap.com/snippets/jquery/alex_valenzuela/1496044