The correct response is:
Around that time, those regions were located in tropical climates that were partially submerged on the coasts.
This observation supports the theory of plate tectonics because it indicates that the continents were positioned differently 300 million years ago, particularly during the time of the Carboniferous period when large coal deposits formed. The formation of coal typically requires warm, humid conditions, which were more prevalent in tropical climates, suggesting that the landmasses that produced these deposits were situated in such environments due to the movement of tectonic plates.