题目内容：

In Chicago, a computerized system has been developed that controls(管理)traffic on the city’s 235 miles of seven expressways. Now one—a controller—can follow the movement of Chicago’s traffic by looking at a set of lights. The system uses electric sensors(感应器) that are built into each expressway, every half a mile. Several times a second, the computer receives information from each sensor and translates it into green, yellow or red lights on a map in the control room. A green light means traffic is moving forty-five miles an hour, yellow means thirty to forty-five miles an hour, and red means heavy traffic—cars standing still or moving less than thirty miles an hour.

  “See that red light near Austin Avenue?”the controller asked a visitor.“That’s a repair truck fixing the road, and the traffic has to go around it.”At the Roosevelt Road entrance to the expressway, the light kept changing from green to red and back to green again.“A lot of trucks get on the expressway there,”the controller explained.“They can’t speed up as fast as cars.”The sensors show immediately where an accident or a stopped car is blocking the traffic, and a truck is sent by radio to clear the road. The system has lowered the number of accidents by 18 percent. There are now 1.4 deaths on Chicago’s expressway for each one hundred million miles traveled, while in other parts of the county there are 2.6.

  Traffic experts say that the Chicago system is the “coming thing”.Systems like Chicago’s are already in use on some expressways in Los Angeles and Houston.“Chicago has taken the lead,”said New York City’s traffic director and he added,“Chicago’s a good example.”

根据短文内容，选择最佳答案，并在答题卡上按要求作答。

1.The passage is mainly about ________ on expressways in Chicago.

  A. the traffic control system                  B. the movement of the traffic

  C. the electric sensors                       D. the traffic lights

2.When the cars move under 30 miles an hour, ________ on the map in the control room.

A. the red light appears                      B. the red light turns yellow

C. the yellow light appears                   D. the green light turns red

3. According to the passage, we may learn __________.

  A. some visitors are traveling on the expressway

  B. there is no heavy traffic on Chicago’s expressways

  C. the traffic on Chicago’s expressways is well managed

  D. the number of accidents in the US has dropped by 18%

4.In Paragraph 2 the underlined word “it” refers to ___________.

  A. the red light                       B. the truck that needs repairing

  C. the traffic                         D. the truck that is fixing the road

5.The writer writes the article mainly by _________.

  A. giving reasons and results           B. giving examples and explaining them

  C. describing what he thinks          D. asking and answering questions