The rubbish _____ is produced every day is becoming a serious problem in cities around the world.
Don’t be late again. Please try your best to be here __________.
While she was trying to pass a truck before her, she __________ another car coming.
---Have you ever been to Shanghai, Mary? ---Yes. I __________ there for a week with my parents last month.
--- __________ came to see you yesterday. ---Who was __________?
I can __________ be a doctor. I don’t have enough patience at all.