The latitude at which heat gain through insolation approximately equals heat loss through terrestrial radiation is at 66∘ North and South. At these latitudes, near the poles, there is a balance between the heat received from the Sun (insolation) during the day and the heat radiated away from the Earth's surface during the night, resulting in a relatively stable temperature regime. This is one of the factors contributing to the formation of the polar climates. So, the correct option is (D):66∘ North and South