Answer: C. Local winds are caused by the unequal heating of Earth’s surface within a small area.
Explanation: In the given paragraph we can see the description of the definition of local winds, why they are formed, and the consequences they bring. The sentence that best states the main point of the text is the corresponding to option C: Local winds are caused by the unequal heating of Earth’s surface within a small area, because it explains the cause of local winds which is the central idea.