While he the letter, he heard a knock at the door.
举一反三
- When he heard the knock at the door, Frank probably thought ___________.
- I heard someone _______ loudly at the door while I was listening to the radio. A: knock B: knocking C: to knock D: knocked
- What did he do when he heard a knock at the doorHe______ he was answering a phone call from a client.
- Suddenly he heard someone（）gently on the window. A: knock B: knocking C: knocked D: to knock
- I was just falling sleep last night when I heard a knock at the door.