Final answer:
Fragmentation of the lithosphere and mantle convection are the factors that make the motions of tectonic plates plausible.
Step-by-step explanation:
The two factors that make the motions of tectonic plates plausible are fragmentation of the lithosphere and mantle convection. The lithosphere, which consists of rigid plates, can break apart into fragments, allowing for plate movement. The asthenosphere, a layer in the upper mantle, is hot and slowly flowing, which also facilitates the movement of tectonic plates.
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