Tell where the sun rays fall perpendiculary only once in a year: a. in north pole circleb. in northern tropicc. in southern tropicd. in south pole circle

Geothermic gradient is the rate of increasing temperature with respect to increasing the depth in the earths interior. away from tech tonic plates boundaries, it is about 25-40 c/km (72-87 degrees f/mi) of depth near the surface in most of the world.

"pacesetter of the south," comma inside the quotes