Questions 17—20 are based on the following passage about the tests of airliner before it goes into service You now have 20 seconds to read Questions 17—20.What’s the main topic of this passage

A．Plants produce their own food but animals don’t.
B．Plant cells have a wall which is non-living in chemical nature but animal cells haven’t.
C．Plants are green but animals aren’t.
D．Plants can’t move but animals can.

A．That you open the recorder.
B．That you get the power supply.
C．That you get the right side of the tape facing you.
D．That you switch the recorder on.

A．They have the power of locomotion.
B．They have a wider range of foods than animals.
C．They are very diverse in their external appearance.
D．They are less sensitive than animals.