Final answer:
The correct answer is one sign. School buses are required to have one sign on the front and another on the back labeled 'School Bus.' Correct option is a.
Step-by-step explanation:
The correct answer is a. One sign. According to the Federal Motor Vehicle Safety Standards (FMVSS), school buses are required to have one sign on the front and another on the back labeled "School Bus." These signs are important for other drivers to easily identify the vehicle as a school bus and take the necessary precautions when driving near it.