I would say it is 'invest'. Investing makes a lot more sense than 'earn', even though both are possible. Raise doesn't make sense. Raising money refers to getting a large sum for a specific purpose. You might need to raise money to pay for an operation, or raise money to start a business. In this case, you already have that sum of money. You want to invest it, and you want a high interest account so that you maximise your interest.

The answer is c. You 'earn' (or make) money.