At the We-Pack Shipping, the workers can unload 28 trucks in 7 hours. Which of the following is a correct unit rate for this situation?
A: 1 truck per hour
B: 4 hours per truck
C: 1 over 4. of a truck per hour
D: 1 over 4. of an hour per truck
A: 1 truck per hour
B: 4 hours per truck
C: 1 over 4. of a truck per hour
D: 1 over 4. of an hour per truck