What is call to action of the movie brave

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?

What is the potential danger from an accident at a nuclear power plant? a) fire and large scale explosions b) exposure to radiation c) meltdown of the plant and surrounding community d) entire cities could be wiped out

Which statement best paraphrase the first line in the prologue