Final answer:
In the context of tractor-trailer maintenance, there should be no space between the upper and lower fifth wheel plates to ensure a secure and safe connection.
Step-by-step explanation:
The question is related to the maintenance and setup of tractor-trailer combinations, specifically regarding the proper spacing between the upper and lower fifth wheel plates. The correct answer here is C) None. There should be no space between the upper and lower fifth wheel plates to ensure a secure connection. When the fifth wheel plates are properly adjusted, they must have enough pressure to keep the connection secure without any gap. A gap can lead to trailer separation, causing a significant safety hazard. Therefore, it is crucial for a tractor-trailer to maintain this standard for safety and optimal operation.