The correct answer is C. Increased use of fans and air conditioners.
During summer months, the demand for electricity increases due to the increased use of fans and air conditioners. This is because people use these appliances to cool their homes and businesses. The increased demand for electricity can lead to power outages if the power grid is not able to meet the demand.
Option A is incorrect because business activity does not typically increase during summer months. In fact, some businesses may experience a decrease in activity during the summer months due to vacations and other factors.
Option B is incorrect because the water supply does not typically change significantly during summer months. The amount of water that is used for irrigation and other purposes may increase slightly, but this is not enough to significantly affect the demand for electricity.
Option D is incorrect because the increased load during summer months is due to the increased use of fans and air conditioners.