bootstrap 4 in Angular 2 dropdown not working

Question

I have followed the following to install bootstrap 4 into my Angular 2 project: Accepted Answer, following the first 1,2,3 and 4 steps

However when I add the following <

Answer 1

The CSS needs to be in the tag.
I quote from bootstrap

Copy-paste the stylesheet into your before all other stylesheets to load our CSS.

I continue quoting

Add our JavaScript plugins, jQuery, and Tether near the end of your pages, right before the closing tag. Be sure to place jQuery and Tether first, as our code depends on them.

Make sure that you have in this way here is the link to bootstrap documentation where i get this quotes https://v4-alpha.getbootstrap.com/getting-started/introduction/

and check this answer in the post that you share the link https://stackoverflow.com/a/39809447/3284537