Which of the Following Is an Example of a Tying

Which of the following is an example of a tying contract?

A) Jon refuses to buy office supplies from any one but Bridget.
B) In order to carry a highly successful organic cleaning compound, Nature's Survival Store has to carry a much less successful line of laundry detergent made by the same company.
C) Traveler's Rest, a travel agency, agrees to buy its insurance need from the Nathan Dean Insurance Agency if the agency agrees to let Traveler's Rest handle the owners' travel plans.
D) A paper supply company agrees to give Harridan Industries a free case of paper towels for every dozen cases it purchases.
E) A salesperson tells a contractor that its paint is mildew-resistant when this is untrue.