//add this class to the html element .text-decoration-underline

bootstrap underline

<a href="#" class="text-decoration-none"> <!-- That is all --> </a>

bootstrap link no underline

<p class="lead"> Vivamus sagittis lacus vel augue laoreet rutrum faucibus dolor auctor. Duis mollis, est non commodo luctus. </p>

bootstrap 4 responsive paragraph