Which of the following is true about speed limit regulations?

Answer: B — They must be observed by law

Speed limits are legal requirements for how fast you may drive. They’re enforceable by law, so you’re expected to stay at or below the posted speed, adjusting for conditions like weather or traffic. Even in emergencies, you don’t have a blanket right to ignore the limit—you should drive safely and follow any directions from authorities, and you may be required to adjust your speed to avoid danger. The other ideas don’t fit because limits aren’t a special rule only at intersections, and they aren’t optional on expressways.