Nine letter adjective that means quickest

You and your friend play a video game where a super bird has to find and eat radiation leaks at nuclear power plants before the plants explode. which of the following is the topic of this video game

Lena has recruited a small group of students to volunteer to clean up the local park. the typeof group that would best serve this purpose is a(a.)informationalb.)learningc.)foc usd.) task

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?