Step 1: Read the question.
We must find the most exact reason why temperature drops as we go from the equator to the poles.
Step 2: At the equator.
Near the equator the Sun's rays fall almost straight down. The heat is packed into a small area, so the ground gets very hot.
Step 3: At the poles.
Near the poles the same rays come in at a slanted angle. They spread over a much larger area, so each spot gets less heat and stays cold.
Step 4: The key factor.
So the real cause is the angle at which the Sun's rays strike the surface. A steep angle means strong heating; a slanted angle means weak heating.
Step 5: Rule out the others.
Wind, ocean currents, and distance from the Earth's center are minor or do not change much with latitude. They are not the main, most precise reason.
Step 6: Conclude.
The most precise reason is the angle of the Sun's rays.
\[ \boxed{\text{Angle of Sun's rays}} \]