An investor has $50,000 in cash to put a $5,000 down payment on 10 different homes valued at $50,000 each and will finance the rest of the investment. Soon after buying the homes she sold all 10 homes for $60,000 each and earned a profit of $100,000 - an astounding 100% return on investment. This scenario is an example of:_________

a. risk-return
b. interest rate spread
c. financial liquidity
d. leverage