题目

There was one thought that air pollution affected only the area immediately around large cities with factories and heavy automobile traffic. At present, we realize that although these are the areas with the worst air pollution, the problem is actually worldwide. On several occasions over the past decade, a heavy cloud of air pollution has covered the east of the United States and brought health warnings in rural areas away from any major concentration of manufacturing(制造业) and automobile traffic. In fact, the very climate of the entire earth may be infected by air pollution. Some7．若a+b+c-2$\sqrt{a}$-2$\sqrt{b-1}$-2$\sqrt{c-2}$=0，求a+b+c的值．