The image below shows a certain type of global wind: The Earth is shown as a circle. Equator is shown and labeled at 0 degrees. 30 degrees north and south latitudes are shown and labeled. 60 degrees north and south latitudes are shown and labeled. Curved arrows are shown pointing from the top and bottom ends of the circle towards 60 degrees north and south latitudes.

What best describes these winds? (5 points)

a
Polar easterlies caused due to sinking, cool air above the poles

b
Polar easterlies caused due to rising, warm air above the poles

c
Trade winds caused due to sinking, cool air above the equator

d
Trade winds caused due to rising warm air above the equator