Про Хуанхэ

[Адов]

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Друг (он учитель) сказал что, 其高峡为镜 значит "黄河在高峡处是一面镜子" Он тоже не уверен. Но думаю, что он правильнее.

Вот так логично:
黄河在高峡处是一面镜子，在平原处是飘舞的丝带。

[Адов]

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1. 凡河川能伸能屈，能收能藏，唯我黄河
For rivers which can stretch and bend, hide and hide , it is only my Huanghe. / Huanghe is the only river which can go straight and crooked and hide itself in mountains or things alike. (I think it is not the fact)

You can just think 能收能藏 as 能收藏. The author deliberately breaks it for 排比 style.

4. 其高峡为镜
She takes the high gorges as mirrors.

I think the reverse (the gorges take the river as a mirror) is better, I don't know why the author say so. But you should know that Huanghe before entering Loess Plateau (黄土高原) is a very clear river.

5. 平原飘带
~ the river meanders on plains like a flying ribbon.

6. 奔川浸谷
sometimes it is running (powerful), sometimes it is soaking the valley (quiet)