A new eight-kilometer road is under construction that links the port area with motorway system. It is expected to carry 20,000 trucks and cars a day, which greatly reduces the overcrowded traffic in the center of the city. As part of the project, two four-kilometer road tunnels are being built below the central area of the city, one for traffic to the north and the other for the traffic to the south. The two tunnels are about 20 meters below the surface and are 12 meters wide, providing for two lanes of traffic in each direction.  In the upper part of the tunnel two air-conditioning pipes remove the waste gas of trucks and cars and keep the quality of air inside the tunnel. The lighting is at the top of the tunnel, practically at its highest point. There will also be electric signs at frequent intervals. They show traffic conditions ahead and can be seen clearly by drivers. The wall is made up of four main elements, which include a waterproofing covering and, on the inside of the tunnel, a concrete lining. Each tunnel is roughly round and the lower part of the tunnel is somewhat flat. The surface of the road lies on the base, which is made of concrete and steel. The drainage system, just below the road surface on one side, removes any extra liquid, particularly water. In the event of fire, the fire main, which is made of steel, pipes water to many fire hydrant stations at regular intervals along the length of the tunnel. The fire main is at the side of the tunnel and at the level of the road surface. Other systems in the tunnel will include emergency phones. 小题1:Each of the tunnels under construction is _____.
A. 1 B. 3 C. 5 D 6 小题3:Driving in the tunnel, one can know the traffic conditions ahead through______.
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