Explanation:

- "Many people may not find the rewards ______ with the time and effort required." Here, we need a word that indicates the rewards are equivalent or match up to the time and effort.

- Option 1: Insignificant

- "Insignificant" means not important or too small to matter. This doesn't fit well with the sentence, as it doesn’t convey equivalency.

- Option 2: Gleeful

- "Gleeful" means happy or joyful. This option doesn't fit logically with the context of comparing rewards to effort.

- Option 3: Cautious

- "Cautious" means careful to avoid danger or harm. This word is not related to the context of rewards matching effort.

- Option 4: Commensurate

- ? "Commensurate" means proportionate or corresponding in size or degree. It fits perfectly with the sentence by expressing equivalence between rewards and effort.