The correct answer is B.
You may be driving at the posted speed limit and still receive a ticket if the posted speed at that particular time when you're driving.
It mostly occurs in : heavy rain or snowstorm, a hail, a hurricane or other natural disaster.
In such cases, it is advisable to reduce your speed and drive under ( or well under ) the posted or recommended speed. It is done as a measure to avoid accidents and unnecessary deaths.
Some other examples when you might receive a ticket for driving at the posted speed limit include: not slowing or accelerating for a passing ambulance or police vehicle and disobeying oral instructions given to you by traffic wardens.