水往底处流是个不可改变的自然法则(law of nature)翻译急

That water always goes down to a lower place is an unchangeable law of nature.或It's an unchangeable law of nature that water always goes down to a lower place.always 是不可缺少的,它反映了必然性

It's an unchangeable law of nature that water goes towards a lower place.

That water flows down to a lower place is law of nature.