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I'm David. I'm an English boy. Now I'm in Wuhan. It's very hot and sunny here. I wear my new cap and T-shirt. But my shoes are old and small. I think I'll get a new pair of shoes on my birthday.
如图,一块厚度、密度均匀的长方形水泥板放在水平地面上,甲、乙两名搬运工人分别用竖直向上的力F甲、F乙使其一端抬离地面.则()