Select the correct active form of the given sentence. A close watch was kept by the police on the bus driver due to his suspicious activities.

• A. The police are keeping a close watch on the bus driver due to his suspicious activities.
• B. A close watch on the bus driver due to his suspicious activities was being kept by police.
• C. The police, due to his suspicious activities, have been keeping a close watch on the bus driver.
• D. The police kept a close watch on the bus driver due to his suspicious activities.