Oh, there’s someone knocking at the door. —_______ must be that naughty boy.

Qian Xuesen tried many times _________ he found the solution to the puzzle about space technology

The discovery of gold in Sahara Desert led thousands to believe that a fortune________

_______ all my letters, I had a drink and went out for a walk.[ ]

rew up in asmall town at the foot of a mountain, the visit to the villagescenes of my childhood