题目

The National Park Service in the United States will mark its one hundredth anniversary in 2016. As it nears its second century, the Park Service plans to increase its educational programs for students and teachers. The plans include transportation support for one hundred thousand students each year to visit national parks to learn about nature and history. Yellowstone is believed to have been the world's first national park when it was established in 1872. Other students will get a chance to see parks in faraway places through Skype and other online programs. The National Park Service als如图，空间四边形ABCD中，M、G分别是BC、CD的中点，则等A.B.C.D.