如何在Bootstrap 4中添加下拉菜单？

Question

I have updating my bootstrap 3 template to bootstrap 4 version. Now problem is sub-menu(drop-down) in my Navigation header not works in bootstrap 4 and it's works in bootstrap 3. How to Add Sub-menu for services list in Bootstrap 4? Here is my code,

<a class='navbar-brand' href='#'>Start Bootstrap</a>
<button class='navbar-toggler' type='button' data-toggle='collapse' data-target='#navbarResponsive' aria-controls='navbarResponsive' aria-expanded='false' aria-label='Toggle navigation'>
  <span class='navbar-toggler-icon'></span>
</button>
<div class='collapse navbar-collapse' id='navbarResponsive'>
  <ul class='navbar-nav ml-auto'>
    <li class='nav-item active'>
      <a class='nav-link' href='#'>Home
        <span class='sr-only'>(current)</span>
      </a>
    </li>
    <li class='nav-item'>
      <a class='nav-link' href='#'>About</a>
    </li>
    <li class='nav-item'>
      <a class='nav-link' href='#'>Services</a>
    </li>

    <li class='nav-item'>
      <a class='nav-link' href='#'>Contact</a>
    </li>
  </ul>
</div>

Answer 1

<div class="dropdown">
  <button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Dropdown button
  </button>
  <div class="dropdown-menu" aria-labelledby="dropdownMenuButton">
    <a class="dropdown-item" href="#">Action</a>
    <a class="dropdown-item" href="#">Another action</a>
    <a class="dropdown-item" href="#">Something else here</a>
  </div>
</div>

Answer 2

@Dinesh Kumar, hopefully this helps you. I've included a codeply project with the working code. It takes your code and adds the following markup after your contact list-item:

...
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="http://example.com" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown link
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
...