Which one of the following provides the force needed to drive the atmospheric circulation ?

• A. Higher biotic content of the tropical latitudes and lower biotic content of the polar latitudes
• B. The energy contrasts between high insolation tropical latitudes and the low insolation polar latitudes
• C. Higher rotational speed of lower latitudes and lower rotational speed of higher latitudes
• D. Equatorial radius of the earth is longer than the polar radius