听力原文: Before a new plane goes into service, every part of it is tested again and again
In the second test, the test pilot must find out exactly what happens when all the engines are shut off at once. He takes the plane up very high. Then he shuts the engines off, the plane begins to fall like a stone. It is the pilot's job to find out how he can control the plane again. These two tests are examples of. how planes are made safe before they ever carry passengers.
What's the main topic of this passage?
A.It's about the tests of a new airliner before its flying.
B.It's about how to protect a new airliner.
C.It's about how to train a new pilot.
D.It's about what the airliner engineers should do.