Concept:A suffix is a group of letters added at the end of a word to change its meaning or grammatical function.Explanation:The suffix ‘-ment’ is added to verbs to form nouns. For example, enjoy+ment=enjoyment and develop+ment=development. Among the options, ‘post’ is a prefix, ‘ed’ is a past-tense suffix but less typical as a noun-forming suffix, and ‘ch’ is not a recognized affix. Only ‘-ment’ clearly acts as a suffix that creates new words.Answer:C. ment