C. a proverb
A proverb is a short staying that tells a universal truth or advice. This proverb is saying that a true friend is one that it there for you in times of need, not just in good times.
An adage is very similar to a proverb. In fact, they can be used interchangeably. Generally an adage is something that is a saying that is very old. Often proverbs are seen as words of advice and an adage as a statement of truth.
A simile is a comparison between two things using like or as.
An idiom is a phrase that does not mean what it says. For example, "raining cats and dogs" is an idiom. This does not mean that cats and dogs are raining down on the earth. It means that the rain is very heavy.
