Which of the following loans would have the lowest total simple-interest charges:
A. A loan for $7,000 at 8 interest for 2 years
B. A loan for $6,000 at 8.5 interest for 1 year
C. A loan for $4,000 at 9 interest for 6 years
D. A loan for $5,000 at 8.75 interest for 4 years