Read the following passage and answer the questions that follow .
Vehicles do not move about the roads for mysterious reasons of their own. They move only because people want them to move in connection with the activities which the people are engaged in. Traffic is therefore a ‘function of activities’, and because, in towns, activities mainly take place in buildings, traffic in towns is a ‘function of buildings’. The implications of this line of reasoning are inescapable.
By ‘this line of reasoning’, the author means

Options

A. to regulate traffic, more policemen have to be employed.
B. to regulate activities, traffic has to be controlled.
C. to regulate traffic, buildings have to be taken into consideration.
D. to understand the traffic problem, we must examine the social context in which it is found.