Four good classmates make an appointment. If both A and B choose to work in the company, D chooses to work in the agency. And only when A chooses to work in the company, C chooses to work in the company. The final result is that both B and D are in company, and all four fulfilled a common agreement. It can be sure that:. ['Only C did not choose to work in the company.', 'Neither A nor C chose to work in the company.', 'Four people have chosen to work in the company.', 'Only A did not choose to work in the company.']