Different points in the earth are at slightly

Different points in the earth are at slightly different distances from the sun and hence experience different forces due to gravitation. For a rigid body, we know

that if various forces act at various points in it, the resultant motion is as if a net force acts on the cm causing translation and a net torque at the cm causing

translation and a net torque at the cm causing rotation around an axis through the cm. For the earth-sun system

(a) the torque is zero

(b) the torque causes the earth to spin

(c) the rigid body result is not applicable since the earth is not even approximately a rigid body

(d) the torque causes the earth to move around the sun