9. An increasing number of experts believe that migrants will exert positive effects on construction of city. However， this opinion is now being questioned by more and more city residents， who complain that the migrants have brought many serious problems like crime and prostitution.
10. Many city residents complain that it is so few buses in their city that they have to spend much more time waiting for a bus， which is usually crowded with a large number of passengers.
11. There is no denying the fact that air pollution is an extremely serious problem： the city authorities should take strong measures to deal with it.
12. An investigation shows that female workers tend to have a favorable attitude toward retirement.