问题
选择题
— Is this a teacher's office?
— Yes, _____________.[ ]
A. I do
B. it is
C. she is
答案
答案：B
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— Is this a teacher's office?
— Yes, _____________.[ ]
A. I do
B. it is
C. she is
答案：B
角，且
=37°，所有接触点和面均不计摩擦。试求小球对墙面的压力F1和对A点压力F2。(sin37°=0.6，cos37°=0.8，tan37°=0.75) 