近年来，沙尘暴一直困扰着人们的生活。尽管人们已经认识到这一可怕的现象，但似乎也没有什么特别有效的办法来防止它。作为一个公民，你认为哪些是防止沙尘暴的必要方法阐明原因。 Sandstorms

A．To justify the study of the Boston University Medical Center.
B．To stress the importance of maintaining proper weight.
C．To support the statement made by York Onnen.
D．To show the most effective way to lose weight.

A．By the nineteenth century, forts were no longer used by the military.
B．Surgeons at forts could not prevent outbreaks of disease.
C．Forts were important to the development of the American West.
D．Life in nineteenth-century forts was very rough.