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问题 填空题

甲乙两种物体的体积之比为2：1，质量之比为2：3．则甲乙两种物体的密度之比为（　　）

A．1：1

B．1：3

C．3：1

D．4：3

答案

密度之比：

ρ甲：ρ乙=

m甲
V甲
：
m乙
V乙
=
m甲
m乙
×
V乙
V甲
=
2
3
×
1
2
=1：3．

故选B．

填空题

请指出所示实验操作中的错误，并改正：

(1)错误：___________________________________________________________________

改正：___________________________________________________________________ 

(2) 错误：_______________________________________________________________

改正：___________________________________________________________________  

(3) 错误：________________________________________________________________

改正：___________________________________________________________________ 
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单项选择题

D


What are you going to do if you are in a burning house How will you escape Do you know how to save yourself Please read the following passage.
Escaping a fire is a serious matter. Knowing what to do during a fire can save your life. It is important to know the ways you can use and show them to everyone in the family, such as stairways and fire escapes, but not lifts.
From the lower floors of the buildings, escaping through windows is possible, learn the best way of leaving by windows with the least chance of serious injury.
The second floor window is usually not very high from the ground. An average(平均高度的) person, hanging by the finger-tips will have a drop of about six feet to the ground. It is about the height of an average man. Of course, it is safer to jump a short way than to stay in a burning building.
Windows are also useful when you are waiting for help. Be sure to keep the door closed. Or smoke and fire may be drawn into the room. Keep your head low at the window to be sure you get fresh air rather than smoke that may leaked (渗) into the room.
On a second or third floor, the best windows for escape are those that open onto a roof. From the roof a person can drop to the ground more safely. Dropping onto cement(水泥) might end in injury. Bushes(灌木丛) and grass can help to break a fall.

Which of the following escaping way is NOT right ( )

A．You can escape though stairways.

B．You can choose fire escapes.

C．Escape from the windows that open onto a roof.

D．Use a lift to come down at onc
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