—You never think of others! You kept me waiting for two hours.
—I'm sorry that you _____ think so.

—Is your brother going to Jack's birthday party tonight?
—I am not sure. He _____ go to the concert with his girlfriend instead.

— Where is Bob? I cannot find him anywhere.
— He _____ have been off long. I heard him make a call just now.

— I've told her many times, and she still forgot about it!
— I understand. It's true that she ____ be very forgetful sometimes.

Great efforts to increase grain production _____ if food shortages are to be avoided.

—  Is there a flight to Paris this evening?
— There ______ be. I'll phone the airport and find it out.