At an air traffic control center, three tasks must be handled: Approach Control, Ground Control, and Tower Control. The following rules apply: 1) If Ben is assigned to Ground Control, then Carla must be assigned to Tower Control. 2) If David is assigned to Approach Control, Ben cannot be assigned to Ground Control. 3) David is assigned to Approach Control. Which of the following statements must be true?
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A
Carla is not assigned to Tower Control.
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B
Ben is assigned to Ground Control.
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C
Carla is assigned to Ground Control.
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D
David is also assigned to Tower Control.