How is the Main Reduction Gear (MRG) characterized?

The Main Reduction Gear (MRG) is characterized primarily by its function in reducing the speed of input from the prime mover (typically a gas turbine or an engine) while increasing the torque before transferring this power to the propeller shaft. This is a crucial mechanism in marine applications where high-speed engines must drive large propellers efficiently.

The characterization as double input, single input indicates that the MRG can accept inputs from multiple engine sources or propulsors. This feature allows for versatility in operation, particularly in scenarios where redundancy or reliance on multiple power sources is desired. The "single output" aspect signifies that there is a singular power path leading to the output shaft, often directing power to the propeller in a marine setting.

In this context, the options that refer to only single outputs or different combinations of inputs do not accurately reflect the typical function and capability of an MRG, which is designed to handle multiple inputs while providing a single line of output for effective propulsion management.