Adjectives are words that modify nouns or pronouns to make them more specific.
There are 3 degrees of adjectives: Positive, comparative and superlative.
The word given is 'rich' which is the positive form of the word. The comparative form of most words is formed by adding '-er' to the original word. The superlative form of the word is formed by adding '-est' to the original word. Therefore, the comparative and superlative degrees of the word 'rich' are 'richer' and 'richest' respectively. Therefore, the correct answer is option C) richer / richest.