When the speed of traffic flow becomes zero,then A. traffic density attains maximum value whereas traffic volume becomes zero B. traffic density and traffic volume both attain maximum value C. traffic density and traffic volume both become zero D. traffic density becomes zero whereas traffic volume attains maximum value

The correct answer is: C. traffic density and traffic volume both become zero.

When the speed of traffic flow becomes zero, it means that the vehicles are not moving. This can happen for a number of reasons, such as a traffic jam, an accident, or a road closure. When the vehicles are not moving, there is no traffic flow and therefore no traffic density or traffic volume.

Option A is incorrect because traffic density cannot attain a maximum value when there is no traffic flow. Option B is incorrect because traffic volume cannot attain a maximum value when there is no traffic flow. Option D is incorrect because traffic density cannot become zero when there are vehicles present.