Explanation:

a short statement of a general truth or rule of conduct

To find the correct one word substitution for the given group of words we must understand the meaning of the words given as options.

1. illustration - the action or fact of illustrating or describing something.

2. maxim - a short, pithy statement expressing a general truth or rule of conduct.

3. instance - an example or single occurrence of something.

4. parable - a simple story used to illustrate a moral or spiritual lesson, as told by Jesus in the Gospels.

Hence it is clear that option 3 is the correct answer. 

Maxim is the substitution for the given group of words.