A law firm has 12 staff members. (1) Some people will use computers; (2) Some people will not use computers; (3) The director will not use computers. Only one of these three propositions is true. Which of the following correctly represents the number of people who will use computers at this law firm? ['2 people will use it.', '2 No one will use it.', 'Only one person will use.', 'Unsure.']