Block to block time is the amount of elapsed time between an aircraft leaving the departure ramp for the purpose of flight and its reaching the arrival ramp at the end of the flight.
选项：

A: Block to block time is the elapsed time since an aircraft leaving the departure ramp for the purpose of flight, until its reaching the arrival ramp at the end of the flight.
B: Block to block time is the amount of elapsed time between an aircraft landing the ramp and departure ramp for the purpose of next flight.
C: Block to block time is the amount of elapsed time since the aircraft starts a heavy maintenance check, until the maintenance check