18._________a US visitor visa twice, the old couple finally gave up their hope of going to America to experience Thanksgiving Day.
In the past twenty years great changes _______in China.
The old city wall ______ in the Ming Dynasty.
The doctors have done ______ they could ______the child.
The teacher asked the students ______ .
I don’t know where I ______ my dictionary, which cost me 50 yuan.