The correct answer is C. Summary.
A synopsis is a brief summary of a longer work, such as a book, article, or movie. It is typically used to provide readers with an overview of the work before they decide whether or not to read it in full.
An index is a list of words or phrases that appear in a book or other document, along with the page numbers on which they can be found. It is used to help readers find specific information quickly and easily.
A mixture is a substance that is made up of two or more different substances. The substances in a mixture can be combined in any proportion, and they do not lose their individual identities.
A puzzle is a problem that is difficult to solve. It can be a physical puzzle, such as a jigsaw puzzle, or a mental puzzle, such as a crossword puzzle. Puzzles are often used for entertainment, but they can also be used to teach people new skills or to improve their problem-solving abilities.