Final answer:
The correct option to complete the sentence 'de agua bajando por el río' is 'Olas cascadas', meaning 'cascading waves'.
Step-by-step explanation:
The correct option to complete the sentence de agua bajando por el río is Olas cascadas. This translates to 'cascading waves' in English. The word 'cascadas' refers to the movement of water down a hill or slope, which is similar to the flow of water in a river.
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