There are numerous ways to compare rivers - by their differences, by their similarities and some of the criteria would be - length, discharge, size, sources, mouth, basin, tributaries, area through which they flow etc. The links below will give you ample details to cover this.
they are rivers
The Amazon, Nile and Mississippi rivers are alike in that they are the longest rivers in the continents in which they are found.
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they all have water
They are alike by the are all the longest and bigest rivers in each of there individual continents
They all are major rivers Also, they are all the largest river on their continents.
they are alike because they are all famous
They are all major rivers.
they're all rivers!