Which of the following best describes a common situs? a an agreement between an employer and a union that requires that the employer stop doing business with another organization b when members of a bargaining unit picket an organization that is owned by the same employer, but that is not a union shop c when members of one union strike in order to support the negotiations of another union that is in a dispute with an employer d a strike that takes place at a location where multiple employers are represented, including those who are not union shops