1 answer
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The correct answers to fill in the blanks are "hotspots" and "stationary."
So the completed sentence would be:
Scientists wondered how volcanoes could be located so far from tectonic plate boundaries until one proposed the idea of **hotspots**, where the magma is much hotter than the surrounding magma. These are **stationary** and do not move with tectonic plates. They are responsible for the creation of island chains.