21. Ladies and gentlemen, please remain ________ until the plane has come to a complete stop.
A. seat B. seating C. to seat D. seated
22. Take care during the holidays! Drinking too much can ________ heart disease and cause high blood pressure.
A. relate to B. contribute to
C. attend to D. devote to
23. As nobody here knows what is wrong with the machine，we must send for an engineer to________the problem.
A. handle B. raise C. face D. present
