| 电气化铁路的输电线常用图所示的方式悬挂在钢缆上．钢缆的A端固定在电杆上，B端连接在滑轮组上．滑轮组由a、b、c三个滑轮构成，配重P由多个混凝土圆盘悬挂在一起组成，配重的总重为G，若不计摩擦和滑轮的重量，则以下说法中正确的是（ ） A．a为动滑轮，B端钢缆受到滑轮组的拉力大小约为3G B．a为动滑轮，B端钢缆受到滑轮组的拉力大小约为 C．a、c为动滑轮，B端钢缆受到滑轮组的拉力大小约为3G D．a、c为动滑轮，B端钢缆受到滑轮组的拉力大小约为  |
答案：A
| 完形填空。 | |||
| My holiday is coming. Yesterday I asked my American friends about the best way to travel within the United States. They said it was best to go by 1 and gave me the 2 . To fly, of course, is the fastest way, but one can't see anything during a 3 except the blue sky and white clouds. So it is not very interesting to one who wants to see the 4 . Besides, airfare is very 5 . To travel by train is 6 , because passengers can walk and buy food and drinks on a train. They can also see cities and the country through the windows. But trains don't leave or 7 at a place every day, and don't go to many cities. To travel by bus, my friends tell me, is easy, cheap and convenient, though not so fast as traveling by plane or so 8 by train. You can find buses almost in every city, big or small. That makes travel arrangement easy. I take their 9 . Now I have decided to go to the east coast with an interesting 10 by bus. | |||
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G
G