—Listen! There is a knock on the door. Who _____ it be?—It must be Jack. Just now I sent for him.

---Must we leave the classroom now?---No, you _____. You _____ leave after the bell rings.

She ______ know the answer, but I’m not sure.

---Must Jack come to sign his name on the paper?---Yes, he_____ .

– Who didn’t turn off the light after school yesterday?– It ______ be Lucy. She told me she was the last one to leave the classroom.