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【多选题】
从总体中抽取样本单位的方法有( )。A.
简单随机抽样
B.
重复抽样
C.
不重复抽样
D.
等距抽样
E.
类型抽样
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【单选题】听力原文： Today when a man steps on to the moon, or something new and important happens, the world learns about it immediately. What did the newspapers say about that first flight in 19037 Strangely enoug...
A.
They were able to fly it in the air.
B.
They were able to stay up in the air for half an hour and more in the machine.
C.
They were able to carry travelers.
D.
They were 'able to fly in mound Dayton.
【简答题】在探究“物体的上浮或下沉与哪些因素有关”的活动中，同学们将新鲜萝卜浸没在水中松手后，萝卜都上浮直至漂浮在水面上，为了使漂浮的萝卜沉下去，小明将一根铁钉全部插入萝卜中，小华也用同样的铁钉，但只将其一半插入到萝卜中，再次将萝卜浸没水中松手，结果两只萝卜均沉入水底.从物体受力的角度来看，他们在萝卜中插入铁钉是为了改变 力的大小，从而使浮力 (填“大于”、“等于”或“小于”)重力；从他们探究的方法来看， ...
【单选题】听力原文： Today when a man steps on to the moon, or something new and important happens, the world learns about it immediately. What did the newspapers say about that first flight in 1903? Strangely enoug...
A.
They were able to fly it in the air.
B.
They were able to stay up in the air for half an hour and more in the machine.
C.
They were able to carry travelers.
D.
They were able to fly in around Dayton.
【简答题】判断正误 （1）浮在水面上的空心铁球，比沉在水底的同体积实心铁球受到的浮力一定大些．（______） （2）当物体所受浮力等于物体的重力时，物体就一定漂浮在液面上．（______） （3）物体上浮时受到浮力大，下沉时受到的浮力小． （______） （4）体积相同的木球和铁球浸没在水中，木球上浮，铁球下沉，在木球没有浮在水面之前，则木球所受的浮力等于铁球所受的浮力．（______） （5）只有上浮...
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