—I bought this shirt for 35 yuan yesterday. —It’s on sale today for only 29. You should have waited. —Oh, really? But how ________ I know?
A survey of the opinions of scientists _____ that three hours of outdoor exercise a week _____ good for our health.
It was last year _____ I visited the museum _____ you had visited.
______ when to leave, I could only stay at home, _____ nothing.
While building a tunnel through the mountain, _____.
— I wonder if I could use your phone for a while? — _____.