(2)Can you often hear the little girl____ in her room? A,sing B,singing 选哪个

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• 1.---Do you smoke?---No,doctors always say that smoking ____ our health.A.is harmful to B.is harmful for C.is harm to D.is harmless to2.He found the book shop ___ of the street.A.in the end B.at the end C.by the end D.on the end3.---Can you hear her ___ in the next room?---Yes.It sounds perfect.A.sings B.to sing C.singing D.is singing4.---May I smoke here?---I am sorry but we do not ____ people ____ any where in the building.A.allow;to somke B.allow;s
• (2)Can you often hear the little girl____ in her room? A,sing B,singing 选哪个
• can you often hear the little girl _in her room A.SANG B,singing c.sung.d.sings
• can you often hear the little girl _in her room A.SANG B,singing c.sung.d.sings
• (2)Can you often hear the little girl____ in her room? A,sing B,singing 选哪个
• 第（1）步怎么到的第（2）步?什么原理?
• 在一连通管两端吹两半径不同的肥皂泡A、B,开通活塞,小泡不断收聚,而大泡则不断变大,最后小泡B缩成一帽顶状,且曲率半径和A同.无论多薄的肥皂泡都是由一定厚度吹成,设内外半径为R1,R2；大气压为P0,泡内气压为P,薄膜内压强为P1,半径越大,内部压强越小,右因为RA>RB,所以PB>PA;所以气体由B流向A,只有当A、B压强相同时,平衡,此时曲率半径相同.曲率半径相同,B只能成帽状.解释完后还是不懂为什么曲率半径相同,B只能成帽状?