Much to my surprise, it _____ raining by the time I wanted to go out. 

This is the first time that I _____ at the meeting.

Years ago we didn't know this, but recent science study ________that people who don't sleep well soon get ill.

— Where is your mother?  —She ________ the shop. She’ll be back in an hour.

— Have you ever visited the Opera House?—Yes．When I was in Sydney, I ______ it twice．