Given the sentence "An ambulance parked on the side of a road with its lights on." is it true that "The drivers are busy."?
Let’s work this out in a step by step way to be sure we have the right answer.
it is not possible to tell
Just because the ambulance is parked at the side of the road with its light on does not mean the drivers are busy.

.

So, the final answer is it is not possible to tell