Which sentence best states the main idea of this passage from Roosevelt's Four Freedoms speech?
Let us say to the democracies: "We Americans are vitally concerned in your defense of freedom. We are putting forth our energies, our resources and our organizing powers to give you the strength to regain and maintain a free world. We shall send you, in ever-increasing numbers, ships, planes, tanks, guns. This is our purpose and our pledge."

A. Americans must be prepared to make sacrifices to win the war. B.The United States must be prepared to thwart an enemy attack. Americans must focus on fixing the problems in their own country.