Answer:
C. Change "was" to "were."
Explanation:
The subjunctive mood indicates a doubt. The verb were instead of was indicates a doubt.
It also indicates a wish , a demand or a suggestion which is contained in the second part of the sentence "I'd use my wealth to make the world a better place".
I'd use my wealth to make the world a better place; is correct
I would use my wealth to make the world a better place" is also correct
the difference of I'd and I would does not make any difference.