When writing a limerick make sure to use:

You have the correct answer. 
Limericks are meant to rhyme they are also meant to be humorous.
 The rhyming part also helps with memorizing the limerick itself :)   

An incentive is a thing that motivates or encourages someone to do something, so the answers should be:

1, 2 and 4. (answers!)

Incentives are a part of the decision process as people will make decisions to further their incentives, so option 3 is wrong.

I hope this helps! :')