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 cranksh
A. Automobiles
B. How a Car Works
C. The First Car
D. Cars and Roads
More than 6000 children were expelled from US schools last year for bringing guns and bombs to school, the US Department of Education said on May 8.
The department gave a report to the expulsions(开除) as saying handguns accounted for 58 percent of the 6093 expulsions in 1996~1997,against 7 percent for rifles or shotguns and 35 percent for other types of firearms.
"The report is a clear sign that our nation’s public schools are cracking down on students who bring guns to school," Education Secretary Richard Rile said in a statement. "We need to be tough-minded about keeping guns out of our schools and do everything to keep our children safe. "
In March 1997, an 11 years old boy and 13 years old boy using handguns and rifles shot dead four children and a teacher at a school in Jonesboro, Arkansas. In October, two were killed and seven wounded in a shooting at a Mississippi school. Two months later, a 14 years old boy killed
A. 10.
B. 9.
C. 12.
D. 22.
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