By Contract,Oil Shale Corporation Forbids Petro Refining,Inc

By contract,Oil Shale Corporation forbids Petro Refining,Inc.,a wholesale buyer of Oil Shale's products,from purchasing the products of its competitors. This exclusive-dealing contract is not permitted

A) under any circumstances.
B) if its effect is to cause a competitor a loss of any business.
C) if its effect is to substantially lessen competition.
D) unless there is no effect on a competitor..