I would personally say the answer is D but I’m not sure !
Many reasons in a free market capitalistic system; their product or service is not in great demand, their product /service is not the best one on the market in terms or quality/price, their product/service does not have enough publicity to sell well, big corporate companies (amazon, walmart, etc.) have a monopoly on most goods and services and sell them at lower prices while underpaying/ overworking workers
D) Subject is the element necessary to complete the sentence above.
You already have a predicate (drives), so you don't need that, or a subordinate/independent clause. What you do need is a subject. For example:
<em>Mercedes </em>drives like no other car.
