I haven’t read the book for __________ long_______I’ve forgotten what it is about

I can’t find my dictionary anywhere.— You _____ have lost it while studying in the library.

There are no people in the hotel. It _______ have the friendliest service.

How was the journey?—Tiring! I caught the train at the last second but all the seatsI stood all the way

You shouldn’t drive for more than three hours without ______ a rest.