HTML show "please fill out this field" message for Radio Field - html

Question

I have a form with several inputs, some text, some radio / dropdown fields. All fields are required. For the text input I get a nice message saying "Fill out this field", but for the Radio and Dropdown fields the message doesn't show. How can I show the error message for radio and dropdown fields? Below is my code:
<form action="" method="post" class="form" role="form">
<div class="form-group required"><label class="form-control-label" for="name">Name:</label>
<input class="form-control" id="name" name="name" required="" type="text" value="">
</div>
<!-- ^ this works -->
<div class="form-group required"><label class="form-control-label" for="gender">Gender</label>
<div class="form-check">
<input class="form-check-input" id="preference-0" name="preference" type="radio" value="male">
<label class="form-check-label" for="preference-0">Male</label>
</div>
<div class="form-check">
<input class="form-check-input" id="preference-1" name="preference" type="radio" value="female">
<label class="form-check-label" for="preference-1">Female</label>
</div>
<div class="form-check">
<input class="form-check-input" id="preference-2" name="preference" type="radio" value="other">
<label class="form-check-label" for="preference-2">Other</label>
</div>
</div>
<!-- ^ this does not work -->
<div class="form-group required"><label class="form-control-label" for="choice">
Please choose "A" or "B"</label>
<select class="form-control" id="which_day" name="which_day" required="">
<option value="a">A</option>
<option value="b">B</option><
</select>
</div>
<!-- ^ neither does this... -->
<input class="btn btn-primary btn-md" id="submit" name="submit" type="submit" value="Next">
</form>

Answer 1

I figured it out now, at least for You need to put "required" at one of the radio / one of the dropdown fields like so:
<div class="form-check">
<input class="form-check-input" id="preference-0" name="preference" type="radio" value="male" required>
<label class="form-check-label" for="preference-0">Male</label>
</div>
And for select fields here is an answer that shows how it can be done.