Answer is A.
When we put any object in between the light source it forms a shadow of that object. The closer the object is to the source of the light, the more light it blocks out, so its shadow is bigger. But if the object is further away, it does not block out much light, and so the shadow is smaller.
Therefore, for the shadow of the ceiling fan to be formed on a wall opposite to the door, the electric bulb must be positioned on the wall having the door.