The correct option is C The 23.5 degrees inclination of the Earth's rotation axis with respect to the plan of the ecliptic
The earth has an axial tilt of 23.5 degrees which means that its rotation axis is inclined to its orbital axis at an angle of 23.5 degrees. This causes one pole of the earth to be directed more towards the Sun on one side of the orbit, and the other pole on the other side. This is the reason for occurrence of 'seasons' on earth.