This is a long river.

这条河很长。

《新英汉大辞典》

Even 100 year old, it may be prolonged in a person's life, but comparing with the long river of history it is quite short.

就算100岁吧，在人的一生中可能是漫长的，但在历史的长河中也是相当短暂的。

youdao

The 1,560-mile-long river originates in the Himalayas and flows across the Uttarakhand state of India to the Bay of Bengal.

这条1560英里长的河流起源于喜马拉雅山脉（Himalayas），流经印度的北安恰尔邦（Uttarakhand state of India），进入孟加拉湾（Bay of Bengal）。

youdao

Then he got up, found a long stick and walked up and down the river bank.

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