It is required that passengers remain ________ when the plane is taking off or landing.

 “This book is ______ more useful for us students.” “Yes, but it is _______ too difficult.”

—How was your recent trip to Sichuan?—I've never had ________ one before.

Yesterday our head teacher made such an　____　speech that we all felt　_____. 

Keeping your body                              your mental health.