在水下气泡内空气的压强大于气泡表面外侧水的压强，两压强差△p与气泡半径r之间的关系为△p= $\frac{2\sigma }{r}$ ，其中σ=0.070N/m．现让水下10m处一半径为0.50cm的气泡缓慢上升，已知大气压强p₀=1.0×10⁵Pa，水的密度ρ=1.0×10³kg/m³，重力加速度大小g=10m/s²．

①求在水下10m处气泡内外的压强差；

②忽略水温随水深的变化，在气泡上升到十分接近水面时，求气泡的半径与其原来半径之比的近似值．

用天平测物体质量：

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    I study at Yu Hong Primary School in Guangzhou. I have forty-seven classmates (同学). Twenty-three are boys and twenty-four are girls. Our classroom is a nice one. It's very big. There are four windows and two doors in it. We have a big blackboard and a small one. The big one is for our teachers and the small one is for us. Mr. Li is our Chinese teacher. He is an old man. We don't like him at all. But Miss Chen, our English teacher, is a young woman. She is very nice. We all like her very much. So we like English the best. We often play basketball with Miss Chen.

如图是人体吸气和呼气时胸廓与隔肌的状态，请分析回答下列问题．