Which is the correct syntax to change the contents of the HTML element with id 'quiz'?

The syntax to change the contents of the HTML element with the id 'quiz' correctly uses the document.getElementById method. This method is specifically designed to access an element in the DOM by its unique id, which ensures that you're targeting the precise element you intend to modify. Once the element is accessed, the innerHTML property can be used to update its content to "New content!!".

In this case, document.getElementById('quiz') identifies the element with the id 'quiz', and setting its innerHTML property effectively changes what is displayed to the user.

Using the method document.getElementsByTagName('p').innerHTML would not work here; this method returns a live HTMLCollection of elements with the specified tag name, but innerHTML cannot be applied directly to a collection without first selecting an individual element. Similarly, referencing quiz.innerHTML assumes that 'quiz' is a globally accessible variable representing the element, which it is not unless defined earlier in the script. Therefore, the correct and reliable approach is to use document.getElementById('quiz').innerHTML.