Last year, John had rented a house in Chicago at $3,000 per month, which was the going market rate at the time. The rental rates in Chicago this year have not changed from last year and John wanted to renew his lease. But, the owner of the house decided to sell it. John liked the house and ended up buying it. So, this year instead of a rent, he is making a monthly payment of $3,500 on his mortgage. For simplicity, assume that the cost of the real estate transaction was $0. As a result of this change in ownership, the monthly contribution of the house to the real GDP of the United States has:

a. declined by $3,000.

b. declined by $500.

c. not changed.

d. increased by $500.

e. increased by $3,000.

f. increased by $3,500.