Which of the following is a valid CSS selector to select all paragraphs on a page?

The choice of "p" as the correct answer is valid because it is the standard CSS selector used to select all <p> (paragraph) elements within the HTML document. In CSS, simple selectors like this are the most direct method of targeting HTML elements for styling. By using "p", you indicate that you want the styles applied to every instance of the paragraph tag.

The other options do not comply with the CSS selector syntax. For instance, "select p" implies a misuse of the "select" keyword, which is not a valid construct in CSS. Similarly, "all p" is not recognized in CSS as a valid selector; there is no built-in keyword "all" in this context. Finally, "paragraph" is only a valid selector if there is a class or ID matching that name. As a standalone term, it does not correspond to any standard HTML element and therefore would not select any paragraphs without additional context that connects it to the HTML structure.