现在完成时的构成为： 。

感知以下课文原句，完成方框下的小题

◆语法感知

1.It has been six years since we last saw each other. 2.You know，I have seen quite a lot of China and I have visited some beautiful cities. 3.Yes，they have just completed it! 4.They have put up a lot of high-rise buildings recently. 5.Our earth has been polluted heavily so far.

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have/has＋过去分词