Under which of the following condition(s) are occluded fronts are created?

 a) When the front remains stationary
 b) When cold air mass moves to to warm air mass
 c) When warm air mass moves to cold air mass.
 d) When an air mass is fully lifted above the land surface.
 Select the correct answer.
 a) 1 and 2
 b) 2 and 3
 c) 3 and 4
 d) 4 only

CAPF 2015

Option (d)