What is the primary purpose of a combine harvester?

The primary purpose of a combine harvester is to gather cereal crops. This machine is specifically designed for the efficient harvesting of grains like wheat, barley, and oats, integrating several functions such as cutting the crops, threshing (separating the grain from the chaff), and winnowing (removing the lighter chaff). The ability to perform these tasks quickly and effectively makes combine harvesters essential in modern agriculture, significantly increasing productivity and reducing labor costs associated with traditional harvesting methods.

In contrast, fertilizing crops, planting seeds, and irrigating fields are distinct agricultural processes that involve different types of machinery and techniques not related to the function of a combine harvester. Fertilizers are typically applied using spreaders or sprayers, seeds are planted with seed drills or planters, and irrigation systems like sprinklers or drip lines are utilized to provide water to crops. Therefore, the correct answer clearly highlights the primary function of a combine harvester in the agricultural process.