What causes areas closer to the equator to have warmer air than the areas farther away?

if you have these answers,

A. The greater angle at which the suns rays strike earths surface at the equator

B. The smaller amount of heat transferred from the sun at the equator

C. The indirect rays of the sun at the equator

D. The concentrated radiation from the sun at the equator

The answer is D. The concentrated radiation from the sun at the equator (Apex)

Because of the tilt of the axis of the earth