阅读理解，根据短文内容,补全下列句子。
When you are in England, you must be very careful in the streets because the traffic  goes on the left.
Before you cross the street, you must look to the right first and then the left.   If the traffic  lights are red,
the traffic must stop.Then the people on foot can cross the road.   If the lights are green,  the traffic cango
and people on foot mustn't cross.
In the morning and in the evening when people go to or come back from work,  the streets are very
busy.The traffic is the most dangerous then.    When you go by bus in England, you have to be  careful,
too. You must always remember the traff'ic moves on the left, so you must be careful. Have a look first
or you'll go the wrong way.    In many English cities, there are  big buses with two floors. You can sit on
the second floor. From there you can see the city very well. That'll be very interesting.
1. Before you cross a street in London, you must look to       .
2. When you drive a car in England, you  must          
3. If the traffic lights are green, the traffic_          .
4. Some buses have two floors, so you can sit on the     .

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