Answer: cost advantage
Explanation: In simple words, cost advantage refers to the advantage earned by the company due to their ability to produce a product at lower cost than others.
In the given case, Carpo inc,. is also the owner of steel and leather companies thus they can make watches at a lower cost as they do not have to bear to profit margin that the external supplier will be getting from them.
Hence from the above we can conclude that the correct option is D.