dropdown menu bootstrap
<div class="collapse navbar-collapse">
<ul class="navbar-nav mr-auto">
<li class="nav-item">
<a class="nav-link" href="#">Clientes</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Fornecedores</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown">
Veículos
</a>
<div class="dropdown-menu">
<a class="dropdown-item" href="#">Carros</a>
<a class="dropdown-item" href="#">Marcas</a>
<a class="dropdown-item" href="#">Modelos</a>
</div>
</li>
</ul>
</div>