Drivers must be careful when driving close to cyclists, and should keep at least feet apart when passing cyclists on the road

Based on what I learned in Driver's Ed, I would say at least 3 feet away. But it really depends what your text book or lesson tells you. Because I might have learned to keep 3 feet away, but your teacher or curriculum might be teaching you to keep at least two feet away. So, I would put 3 feet, but before you put that answer, double check for yourself in your text book or lesson.

 Drivers must be careful when driving close to cyclists, and should keep at least 3 feet apart when passing cyclists on the road.