【单选题】

Questions 17--20 are based on the following passage. You now have 20 seconds to read Questions 17--20. What’s the main topic of this passageA．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.