[单项选择]Before a new type of airplane goes into service, every part of it is tested again and again. But there are two tests that are more important than all the others.
The first is called the "tank test". A modern airplane must fly very high in the sky. Air must be pumped into the plane so that the passengers can breathe. The metal structure(结构) of the plane has to be very strong for this reason. When the plane is filled with air, the air presses against the skin of the plane inside. The pressure (压力) on a small window is like a huge foot that is trying to get out. If a small part of the plane were to fail, the plane would explode in the sky. To test the structure of the plane, the plane is lowered into a huge tank or container of water. Then it is filled with air. The pressure inside the plane is greater than it ever will be when it is high up in the air. Finally, there is an explosion. This does not cause so much damage inside the water tank as it would anywhere else. Engineers can di
A. the amount of air in the plane
B. the strength of the plane structure
C. the pressure inside and outside the plane
D. the power of the airplane engines

[单项选择]Before a new type of airplane goes into service, every part of it is tested again and again. But there are two tests that are more important than all the others.
The first is called the "tank test". A modern airplane must fly very high in the sky. Air must be pumped into the plane so that the passengers can breathe. The metal structure(结构) of the plane has to be very strong for this reason. When the plane is filled with air, the air presses against the skin of the plane inside. The pressure (压力) on a small window is like a huge foot that is trying to get out. If a small part of the plane were to fail, the plane would explode in the sky. To test the structure of the plane, the plane is lowered into a huge tank or container of water. Then it is filled with air. The pressure inside the plane is greater than it ever will be when it is high up in the air. Finally, there is an explosion. This does not cause so much damage inside the water tank as it would anywhere else. Engineers can di
A. It will be broken.
B. It will be made stronger.
C. It will be filled with water.
D. It wilt be tested by pilots.

[单项选择]

Before a new plane goes into service, every part of it is tested again and again. But there are two tests that are more important than all the others. In the first test, a modern airliner must fly at very high altitudes. Air must be pushed into the airliner so that the passengers can breathe. The metal structure of the plane has to be very strong for this reason. When the airliner is filled with air, the air presses against the skin of the plane inside. The pressure on a small window, for instance, is like a huge, giant foot that is trying to get out. If a small part of the plane were to crack, the plane would explode in the sky. It is lowered into a huge tank of water to test the structrue of the plane. Then it is filled with air. The pressure inside the plane is greater than it ever will be when it is in the air. Finally, there is an explosion. Engineers can discover which part of the plane has cracked.
In the second test, the test pilot must find out exactly what happe
A. Because without air the plane can’t fly.
B. Because the plane needs air for its fuel.
C. Because the passengers’ lives depend on air.
D. Because the passengers have paid for it.