叠罗汉是一种二人以上层层叠成各种造型的游戏娱乐形式，也是一种高难度的杂技．如图所示为六人叠成的三层静态造型，假设每个人的重量均为G，下面五人的背部均呈水平状态，则最底层正中间的人的一只脚对水平地面的压力约为（ ）
A．
G3 4
B．
G7 8
C．
G5 4
D．3 2G 
最上面的人受到的竖直向下重力为G，所以每个腿上的力都是
．G 2
中间层最左边的人，受到竖直向下的力为：G+
=G 2
，所以每个腿上的力都是3G 2
，由对称性，中间层最右边的人每个腿上的力也是3G 4
．3G 4
最底层中间的人，受到竖直向下的力为：G+
+3G 4
=3G 4
．所以其每根腿上的力为：5G 2
．5G 4
即：最底层正中间的人的一只脚对水平地面的压力约为：
G．故C正确，A、B、D错误．5 4
故选C．
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| One day a teacher asked her students to list the names of 1 students in the classroom on two sheets of paper, leaving a space between each name. Then she told them to think of the 2 thing they could say about each of their classmates and write it down. It 3 the class some time to finish their assignment, and as the students left the room, each one 4 the papers. That Saturday, the teacher wrote down the 5 of each student on a separate sheet of paper and 6 what everyone else had said about that individual. On Monday she gave each student his or her list. Before long, the whole class was 7 . "Really?" she heard whispered. "I never knew that I 8 anything to anyone!" and, "I didn't know others liked me so much" were most of the comments. No one ever 9 those papers in class again. She never knew if they discussed them after class or with their parents, but it didn't 10 . The exercise had completed its 11 . The students were 12 with themselves and one another. That group of students moved on. Several years later, one of the students was 13 in Vietnam War and his teacher 14 the funeral of that special student. After the funeral, most of Mark's former classmates left. Mark's mother and father were there, obviously waiting to speak to his teacher. "We want to 15 you something," his father said, taking a 16 out of his pocket. "They found this on Mark when he was killed. We thought you might 17 it." Opening the wallet, he 18 removed two worn pieces of notebook paper that had obviously been taped, folded, and refolded many times. The teacher knew without 19 that the papers were the ones on which she had listed all the good things each of Mark's classmates had said about him. "Thank you so much for doing that," Mark's mother said. "As you can see, Mark 20 it."
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