He recognized me _____ he saw me.
What was considered impolite years ago has become ________now.
Which way do you enjoy _______ the coming winter holiday, staying home or going on a trip to Europe?
_______ worries the public a lot the way the students are getting more and more stressed out.
The Tenth Art Festival held in Jinan _______ to many people from the world.
According to the agreement, nobody _______ let out how they spent the three days in the cave.