The past 30 years has ______ the great changes that have taken place in China.

All of us still remember the terrible earthquake that______Tangshan twenty years ago.

 Lacking rain, many river in Yunnan province have ______ recently.

Mr. Brown repeated his words to his son, raising his voice a bit, but still        no answer. 

Tom _______ the TV set for $500，which was much cheaper than he had expected．