When Monarch Butterflies Arrive in Mexico from Canada and the United

When monarch butterflies arrive in Mexico from Canada and the United States, they converge on oyamel fir trees. The trees provide shelter to monarch butterflies they are also essential to the communities that surround the forests. In the past, residents used the wood for cooking and heating, but recently, they have began to sell it in order to support their livelihoods. As a result of logging oyamel fir trees, the habitat of the monarch butterfly population has shrunk.
What is the main idea of this passage?

A) Because of an increase in harvesting of the ovamel fir tree, the monarch butterfly population in North America has decreased sharply.
B) Monarch butterflies migrate from Canada and the United States to Mexico, where they spend the winter in a fir-tree forest.
C) Scientists predicted that monarch butterflies will soon become endangered, then extinct.
D) The economic crisis has caused Mexican land owners to harvest ovamel fir trees for sale, rather than only for personal use.