What event occurs when the HTML is fully downloaded?

The correct answer identifies that the event occurring when the HTML is fully downloaded is when the last byte of the current page is received. At this point, the download of the entire HTML content is complete, which means the content is ready for further processing.

Once the last byte is received, the browser can then parse the HTML, build the Document Object Model (DOM), and eventually render the page to the user. This completion of the download is crucial because it signals that all the content intended to be displayed is now available, allowing the browser to begin the subsequent processes of rendering or executing any scripts included in the HTML. This event marks a definitive point in the page loading process, establishing that all necessary HTML has been received before any interaction or rendering can take place.

The other choices represent different stages or aspects of the web page loading process. The reception of the first byte indicates the start of the response, the document being ready for user interaction suggests that rendering is complete, and the browser beginning to render the page relates to a step in the rendering process rather than the completion of HTML download.