请根据下面短文回答： —Buses leave the Railway Station, New York City, from 7:00 a.m. and then every half-hour, until 11:30 p.m. (7 days a week) —Evening rush-hours(5:00 p.m. to 7:00 p.m.): Buses leave the Railway Station, New York City, every 15 minutes. (Monday to Friday) —Holidays: Buses leave every hour on the hour. (Trip time: 30 minutes each way) —All tickets must be bought at Window 12, the Railway Station, New York; or at the Brennan Station Window. What does it mean by "Buses leave every hour on the hour"
A．Buses leave every two hours. B．Buses leave every one and half hours. C．Buses leave every hour such as nine o’clock, ten o’clock, and so on.