When may a driver use the left lane of a highway for passing?

Answer: B — When the vehicle in front is going significantly slower than the speed limit

Drivers should use the left lane for passing when the vehicle in front is going significantly slower than the speed limit, as this helps maintain a smooth flow of traffic and allows for faster drivers to safely overtake slower drivers. Option A is incorrect because drivers should never solely rely on the instruction of a law enforcement officer to determine when to use the left lane for passing. Option C is incorrect because on multiple-lane highways, the left lane can be used for passing at any time, not just at night. Option D is incorrect as there are certain circumstances where using the left lane for passing is necessary and safe.