阅读短文，选择正确答案。
The Sea
What do you know about the sea? Some people have seen it but others haven't. The sea looks beautiful on
a fine sunny day and it can be very rough when there is a strong wind. What other do you know about it?
Of course, the sea is very large. In the world there is more sea than land. If you have swum in the sea, you
know that the sea is salty. Rivers carry salt and the land into the sea. Some places of the sea are saltier than the
other places. Do you know the Dead Sea? It is so salty that you can't sink when you are swimming in the water!
And fish cannot live in it!
1. people have been to the sea.[ ]
A. Some
B. All
C. Only a few
D. Very few
2. The sea looks beautiful in .[ ]
A. the morning
B. bad weather
C. windy days
D. fine weather
3. The salt in the sea comes from .[ ]
A. the Dead Sea
B. the land
C. a river
D. the rock under the sea
4. Fish cannot live in the Dead Sea because .[ ]
A. the sea is dead
B. the water is too salty
C. there is no salt in it
D. fish don't like the name
5. Which of the following is TRUE?[ ]
A. There is more land than the sea in the world.
B. There is no salt in some places of the sea.
C. None of the people can swim in the Dead Sea.
D. People can swim in the Dead Sea more easily than in other places.
物体，它们的大小相对于轨道来说可忽略。光滑轨道ABCD中的AB部分水平，BC部分为曲线，CD部分为直径d=5m圆弧的一部分， 该圆弧轨迹与地面相切，D点为圆弧的最高点，各段连接处对滑块的运动无影响。现松开P物体，P沿轨道运动至B点，与Q相碰后不再分开，最后两物体从D点水平抛出，测得水平射程S=2m。
) 求：
