Hello there!
Your question asks what the goal of an economist who makes new theories is.
Answer: C). contribute to an understanding of how the world works
The reason why answer choice " c. contribute to an understanding of how the world works" is the correct answer because this is specifically the goal of an economist who makes new theories.
What an economist does is study economics. They pretty much study the way goods are distributed around the world, traded, etc.
Economists would need to understand how the world works in order to make theories, due to the fact that their theories are based upon what's going on in the world. If an economists doesn't know what's going on in the world, then their theories would be unreliable, and probably would not be on topic with what's going on in "modern-day" economics.
I hope this helps!
Best regards, MasterInvestor