how to make dropdown menu using bootstrap code example

Example 1: bootstrap 4 dropdown

<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>

Example 2: dropdowns

There are 2 dropdowns
1- HTML
2- SELECT

we determine what kind of dropdown it is
 -By tagName.We inspect.If it has <select> tag, it means it is <select> dropdown. 
 -If it is HTML, we can locate and click just as any other web element.
 
 I handle Select type of dropdown by using Select class from Selenium. 
    - Methods to select from dropdown:
        - selectByVisibleText
        - selectByValue
        - selectByIndex 
        
I verify which option is selected in a dropdown?
 - If we want to get the currently selected option, 
 we use getFirstSelectedOption() method.
        -> return type: currently selected option as a web element
        
--> .getOptions();
    -> This method will return all of the options in the <select> web element.
    -> return type: List<WebElement>