To live on Mars, you need to wear boots which ________ to prevent you from floating off into space.
-- How about ____ Christmas evening party? -- I should say it was ____ success.
— Would you like to go hiking with us? — ________. I’m preparing for the coming exams.
— Excuse me, could you tell me ________ to fly to Guilin? — About two hours.
The boy isn’t old enough ________ with the difficult problem by himself.
Not only Susan but also Sandy _________ abroad for traveling. They will return next Sunday.