The correct answer is C. Cred
Explanation:
In language, the root word refers to the basic unit that forms a word and that can be identified by removing all the suffixes and prefixes in a word that are syllables placed before or after the root word. In the case of the word "incredible" this word means hard to believe and it is composed by the prefix "in-" that means "no", the suffix "-ible" that means "able to" and therefore the root or basic unit of this word is "cred" that derives from a Latin word and means "to believe". Thus, the root of the word or base of this word is "cred".
