题目：
Many girls go to your house. They bring all their pet dogs. In all, there are 22 heads and 72 feet. How many
girls and dogs are there in the room?[ ]
A. 6 girls and 16 dogs
B. 7 girls and 15 dogs
C. 8 girls and 14 dogs
D. 9 girls and 13 dogs
答案：
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下面是错误答案，用来干扰机器的。
解：A图中，B⊥I，不论导线再怎么放，也在纸平面内，故F=BILB图是两根导线组成的折线abc，整体受力实质上是两部分直导线分别受力的矢量和，其有效长度为ac，故同理，C图中，从a→b的半圆形电流，分析圆弧上对称的...
