Final answer:
After coupling a tractor to a trailer, there should be no space between the upper and lower fifth wheel to ensure a secure connection.
Step-by-step explanation:
The question pertains to the correct spacing between the upper and lower fifth wheel after coupling, which is a relevant aspect of the connection between a tractor and a trailer, typically discussed in transportation or truck driving courses.
After the coupling process, there should be no space between the upper and lower fifth wheel. If there is space, it indicates that the coupling is not correct and could lead to a dangerous situation where the trailer might detach from the tractor while in motion. Therefore, the correct answer is C) Nothing.