题目内容：

根据句意，用括号内所给单词的适当形式填空。

1.The computer is considered as one of the most important _________（invent）in the 20th century.

2.The UK is an old _________（Europe）country, where there are many palaces and castles.

3.The underground has been in _____________（serve）since last May.

4.The athlete came first with a run of 9 seconds in the men’s 100-metre race. He has become the __________ （proud）of us Chinese.