Part iii To encourage people to take public transit, the government runs a program which provides free transit passes for a month. The 600 residents who drive to work are invited to participate in the following experiment. Half of the urban residents who drive to work are randomized to receive the free pass for one month and half do not receive such free pass. The rural residents who drive to work are randomized in a similar fashion. After six months, the proportion of urban residents who switch to taking public transit is compared between the free-pass and no-free pass groups. The same comparison is also done among the rural residents. In the experiment described above, area of residence (urban versus rural) [CHECK ALL THAT APPLY] A. is the response variable. '7' B. defines the treatments. '7' C. is the blocking variable. '7' D. defines the experimental units. '7' E. none of the above