<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
</head>
<body>
<form action="/form/submit" method="post">
<select name="books" required>
<option value="">Books</option>
<option value="html">HTML</option>
<option value="css">CSS</option>
</select>
<input type="submit">
</form>
</body>
</html>