Here's a problem to solve: John drove a truck for one hour at a rate of 80 kilometers per hour. The next hour, he drove at 100 kilometers per hour. What was his average speed during those two hours?

Among the 4 following options, which is the correct answer?

- A: 80 kilometers per hour
 
- B: 90 kilometers per hour
 
- C: 100 kilometers per hour
 
- D: 180 kilometers per hour
 