The element is the correct HTML tag for attaching external resources, most commonly an external CSS stylesheet. When used for this purpose, it is placed within the document's section. The rel attribute must be set to "stylesheet", and the href attribute must contain the URL of the CSS file to be linked. This method is the standard practice for applying external styles to a web page.

A. <style> is used to embed CSS rules directly within an HTML document (internal CSS), not to link an external file.

C. <script> is used to embed or reference executable scripts, typically JavaScript, not CSS stylesheets.

D. provides metadata about the HTML document, such as character set or viewport settings, but does not link external resources.

- Mozilla Developer Network (MDN). (n.d.). : The External Resource Link element. In HTML: HyperText Markup Language. Retrieved from https://developer.mozilla.org/en-US/docs/Web/HTML/Element/link. (See "Linking to a stylesheet" section).

- WHATWG. (n.d.). 4.2.4 The link element. In HTML Living Standard. Retrieved from https://html.spec.whatwg.org/multipage/semantics.html#the-link-element. (See example under "4.2.4.2. Processing the rel attribute").

- W3C. (2011, May 25). CSS basics. In CSS Snapshot 2010. Retrieved from https://www.w3.org/TR/CSS2/intro.html#q1.