I think the answer is C but i could be wrong
The answer to the first analogy (mystery:clue :: eraser:) would be letter d. open. Mystery is to clue while eraser is to open. The answer to the second analogy (habit: custom :: extravagant: ) would be letter c. lavish.
Answer: Horace Mann invented school. The main reason we attend school is to gain the skills and education needed to live autonomously and successfully.
Hope this helps!