Professor Jordon is well known for his _____ into the habits of the common housefly.
I ______ along the road when I saw Peter. So we stopped and had a chat.
Betty will ring me up as soon as she ______ in Beijing.
The teacher requested that we ______ the classroom after using it.
The moment I met you, I ______ you though I hadn’t seen you for about ten years.
No one can imagine the difficulty he had ______ playing computer games.