How do you judge wheather a conclusion is succesful

But we pulled at the grill [on the ground] and it gave way. and then we saw iron rings as steps leading down a shaft into a darkness without bottom. … it was a great tunnel. its walls were hard and smooth to the touch; it felt like stone, but it was not stone. on the ground there were long thin tracks of iron, but it was not iron; it felt smooth and cold as glass. we knelt, and we crawled forward, our hand groping along the iron line to see where it would lead. but there was an unbroken night ahead. what is the most likely explanation for the walls described in the bold text?

Which sentence uses the verbs correctly?

Stop pause the type of tectonic plate movement that occurs due to forces of a mantle convention and result in the subduction of lithosphere causinga. hot spotsb. rift valleys c. ocean trenches d. mid ocean ridges