has down是什么时态

　　The name has come down from the last century.

　　这名称是从上个世纪流传下来的。

　　Notice how the tread on this tyre has worn down.

　　注意这个轮胎的花纹磨损的程度。

　　Our youngest boy has gone down with chickenpox.

　　我们的小儿子染上了水痘。

　　He has climbed down on pledges to reduce capital gains tax.

　　他已经作出退让，许诺降低资本收益税。

　　He has gone down considerably in my estimation.

　　我对他的评价已经一落千丈。