.You’ll never guess who I met today—my old teacher! We_____for twenty years.

Before the first nonstop flight made in 1949,it______necessary for all planes to land for refueling.

I ______ Beijing for Shanghai in a few days. Do you know when the earliest plane ________?

Prices____ all the time and no one knows when they         stable.

After he had won the first prize, Mr. Su ____ to a restaurant to celebrate with us.