Final answer:
School zone signs are warning signs with posted operation hours and flashing lights to ensure the safety of crossing students. The correct answer is option: b) Warning.
Step-by-step explanation:
School zones are indicated by warning signs with the posted hours of operation and flashing yellow lights advising caution. These signs serve to alert drivers to the presence of an area where children are likely to be crossing the road to get to or from school.
It is crucial for the safety of students and other pedestrians that drivers adhere to the reduced speed limits and exercise increased vigilance when these signs are present, especially during the hours specified on the signs when children are most likely to be present.