Is it permitted to place curtains on the rear windows of a vehicle?

Is it permitted to place curtains on the rear windows of a vehicle?
A)No, it is prohibited.
B)Yes, if it is a type-approved accessory.
C)Yes, if the vehicle has an exterior rear-view mirror on each side.Correct
The glazed surface of the vehicle must in all cases allow the driver adequate visibility of the entire road, without interference from films or adhesives. Circulating with adhesive films or curtains on the rear windows will only be permitted when the vehicle has two exterior rear-view mirrors.