No.
The speed of sound in water depends on the temperature and pressure. As you go deeper, the pressure increases and the speed of sound increases.
The one answer that I am missing among the options, but which is the correct one is: the geography of the region ( I assume that that's what was instead of the "7" in the first option).
It was very mountainous, with valleys and islands on which people lived -meaning there was a natural separation between the different settlements.
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