He was last seen _________in his office at about 7:15 p.m..
He was so busy ____ his homework that he forgot to have supper.
Going _____ the crowd of people isn’t an easy thing.
Could you give me _____ advice on how to learn English well?
—Excuse me, _____ is Dalian from Beijing ?—It’s about three hours by car.
Li Lei likes playing sports. He always spends 40 minutes ______ basketball after school every day.