Answer: D) Diacritical marks.
Explanation: A Diacritical mark is a symbol added to a letter, to alter its pronunciation, meaning or function. It is also known as an accent mark. In English are usually use to indicate special sounds normally in foreign words that are imported from other languages, like "cliché" and "café" that are french words, and the diacritical mark points out that the final "e" is pronounced.