练习：
1. Paragraph 3
2. Paragraph 4
3. Paragraph 5
A The Main Components of the Maglev Train System
B High-speed Maglev due to Zero Friction
C The Working Principle of the Maglev Train
D Differences between Polarity and Magnetic Field
E Comparison of Maglev Trains with Traditional Ones
F Maglev with a Powerful Motor
4. Paragraph 6
5. Several countries in the world are using strong electromagnets
6. You can connect a wire to the positive and negative ends of a battery .
7. A unique system of magnetic fields is created by the coils
8. The frictionless maglev train enables you
A to develop a maglev train rail system
B To explain why maglev trains are faster
C to pull and push the train forward
D to create a magnetic field
E to experiment with the maglev train
F to travel from Paris to Rome in about two hours