Which of the following sentences is an effective thesis statement？

A.Immigrant workers are working in dangerous conditions and are doing the jobs that no one else is willing to do.

B.Fast food advertising not only targets the children’s parents， but the children themselves.

C.Fast food industry has had an effect on community by implementing its workers to low wages and have poor working conditions as in slaughterhouses.

D.The development of steel was very important in the growth of a distinctively new architecture both in Europe and in North America.

正确答案：The development of steel was very important in the growth of a distinctively new architecture both in Europe and in North America.