The correct answer is: D. All follows.
The statement says that any further increase in the pollution level in the city would pose a severe threat to the inhabitants. This means that we need to take steps to reduce pollution. The three courses of action all suggest ways to reduce pollution.
Course of action I suggests that all the factories in the city should immediately be closed down. This would reduce the amount of industrial effluents being released into the environment.
Course of action II suggests that the automobiles should not be allowed to ply on the road for more than four hours a day. This would reduce the amount of automobile exhaust being released into the environment.
Course of action III suggests that the Government should restrict the issue of fresh licences to factories and automobiles. This would reduce the number of factories and automobiles in the city, which would in turn reduce the amount of pollution.
Therefore, all three courses of action would help to reduce pollution and protect the inhabitants of the city.