晴朗无风的早晨，当飞机从空中飞过，在蔚蓝的天空中会留下一条长长的“尾巴”，如图所示，这种现象俗称为“飞机拉烟”．产生这一现象的原因之一是飞机在飞行过程中排出的暖湿气体遇冷所致．在这一过程中，暖湿气体发生的物态变化是（ ）
A．熔化
B．液化
C．蒸发
D．升华
发动机排出的暖湿热气体遇到高空冷空气，使暖湿热气体温度降低液化成小水滴形成的白色雾气，此过程属于液化现象．
故选B．
Sam goes home from school. He’s hungry(饿的).And he has a lot of homework. He wants to see Mike and 26 football, too. He doesn’t have 27 time. “Hello，Sam，”says Mrs Green.“ 28 is school today? ” “Fine. But I have a lot of homework，and I’m hungry. ” “There are some apples on the table.” “No，I don’t want any 29 . Is there 30 cake? ” “Yes. But please 31 eat too much.” Sam eats some cakes. Then he sits(坐) 32 at the table. He opens his book and begins to write. Mrs Green 33 to the shop. Mrs Green comes back 34 the shop. Sam is 35 . Mrs Green says，“My son，you’re a good boy.”
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