An increasing number of experts believe that migrants will exert positive effects on construction of city 。 owever， 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.
越来越多的专家相信移民对城市的建设起到积极作用，然而，越来越多的城市居民却怀疑这种说法，他们抱怨民工给城市带来了许多严重的问题，象犯罪和卖淫。
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.
无可否认，空气污染是一个极其严重的问题：城市当局应该采取有力措施来解决它。
An investigatio
