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  3. The first automobile was invented more than two hundred years ago. It used steam for power and had wooden wheels. The first auto

The first automobile was invented more than two hundred years ago. It used steam for power and had wooden wheels. The first auto

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问题     The first automobile was invented more than two hundred years ago. It used steam for power and had wooden wheels. The first automobile may have been simple and primitive, but it was an extremely important invention. The automobile today is the primary means of land transportation. It has produced more changes in our daily life than any other machines.
    Almost all gasoline engines work in the same way—with four movements, or strokes, of a piston in a cylinder. The first stroke pulls the fuel mixture (gasoline and air) into the cylinder. The second stroke compresses the fuel mixture. A spark plug produces a spark that ignites the fuel mixture and causes the third stroke. The final stroke removes any waste gases which might remain in the cylinder.
    The preceding paragraph explains what happens inside the cylinder to make the piston move. When the piston is pushed down by the explosion in the third stroke, it pushes the connecting rod. This rod rotates the crankshaft. The crankshaft is connected to other parts which turn the wheels. Most cars today have four, six, or eight cylinders.  
Good title for this selection is ______.
选项 A、Automobiles
B、How a Car Works
C、The First Car
D、Cars and Roads
答案B
解析 本题属主旨判断题。文章第一段主要讲：第一辆汽车的重要性，第二、三段主要讲：汽车是怎样发动起来的。
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