The answer is ‘All the above’.
The combine harvester, or simply combine, is a machine designed to grow a number of agricultural crops effectively. The word derives from the combination of three distinct winnowing, threshing and reaping activities in a single process. Combine is the machine that does the cutting of standing crops and recovers the grain also.
Winnowing is a process used to separate grains from the chaff by removing the scaly inedible chaff surrounding the grain. A machine called Combine is used for this process. The combine is a mixture of harvester and thresher.
So, the correct option is (D)