Question

It had previously come to me that this ivory leg had at sea been fashioned from the polished bone of the sperm whale’s jaw. How is the fact that Ahab’s leg is made from whale bone significant to the novel’s theme of man versus nature? It signifies that Ahab has pitted himself against nature in an effort to dominate it. It signifies that Ahab lives a life in harmony with the natural world. It signifies that Ahab has made a choice to surrender to the power of the whales he hunts. It signifies that Ahab see himself as an equal and dependent part of a greater whole.

Answer 1

The correct answer is - it signifies that Ahab has pitted himself against nature in an effort to dominate it. 
He spent his entire life chasing after whales, wanting to hunt them down, and especially one whale named Moby D.ick, who bit off his leg. He wanted to dominate over nature, which is why he tried to show it that he could by having an artificial leg made of whale bone. However, no man can be more powerful than nature, which is something Ahab saw at the end.

Answer 2

It signifies that Ahab has pitted himself against nature in an effort to dominate it.