The correct answer is option 1, pressure gradient. Wind speed is controlled by the pressure gradient, which is the rate of change of pressure over a distance. In areas where there is a large difference in pressure over a short distance, such as between a high-pressure system and a low-pressure system, wind speed tends to be stronger. This is because air moves from areas of high pressure to areas of low pressure in order to equalize the pressure. The greater the pressure difference, the faster the air moves and the stronger the wind. Option 2, rotation of the earth, affects wind direction through the Coriolis effect, but not necessarily wind speed. Option 3, insolation (sun`s radiation), can influence temperature and atmospheric pressure, which in turn can affect wind patterns, but it does not directly control wind speed. Therefore, option 1 is the most accurate answer. Alert - Correct answer should be option 4.