Is cow common or proper noun?

True of false hearing loss can range from mild to profound

As oil prices rose during 2006, demand for alternative fuels increased. ethanol, one alternative feul, is made from corn. according to an article in the wall street journal the price of tortillas which are made from corn also rose during 2006. the price spike in tortillas is part of the ripple effect from the ethanol boom. draw demand and supply graph for corn market and use it to show the effect on this market of an increase demand for an ethanol. be sure to indicate the equilibrium price and quantity before and after the increase in demand for ethanol.

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?