Complementary cells occur in ‘lenticels’.
Lenticels are aerating pores in the bark of woody plants for the exchange of gases. The lenticels appear on the surface of the bark as raised scars containing oval or rounded depressions. Lenticels are large sized aerating pores present in the cork tissue for gaseous exchange. Mainly they function to help in the exchange of gases
So, the correct option is (c)