Margaret Tells the Members of the Raleigh Association of Restaurant

Margaret tells the members of the Raleigh Association of Restaurant Owners that they will be able to get a better price on linen supplies (tablecloths, napkins) if they will deal with one supplier rather than split their business between two. They all know Margaret deals with Niagara Linen rather than Cayuga. Under the Sherman Act, if they all sign contracts with Niagara:

A) there is no violation since there is no express agreement to boycott Cayuga.
B) illegality may be implied from this conduct.
C) there is no concerted action.
D) this is horizontal market allocation.