Buses run between Alphatown and Betatown, a distance of 25 km. Buses set off from Alphatown every 20 minutes at 0, 20 and 40 minutes past each hour. The return journey from Betatown also goes every 20 minutes, starting at 10, 30, and 50 minutes past each hour. The buses travel at a steady 60 km per hour both ways. It is noted that in Hornville, on the route, buses going opposite ways pass and the drivers acknowledge each other. Which one of the following would explain why the buses meet in Hornville?

A. Hornville is either 5 km from Alphatown or 5 km from Betatown.

B. Hornville is either 7.5 km from Alphatown or 7.5 km from Betatown.

C. Hornville is either 10 km from Alphatown or 10 km from Betatown.

D Hornville is 12.5 km from Alphatown and 12.5 km from Betatown.