There are two graphs. Both graphs measure Aircraft Carriers on the vertical axis and Automobiles on the horizontal axis. The left graph shows that on production possibilities frontier A, 0 automobiles and 400 aircraft carriers can be made, or 400 automobiles and 200 aircraft carriers, or 600 automobiles and 0 aircraft carriers. The left graph also shows that on production possibilities frontier B, 0 automobiles and 500 aircraft carriers can be made, or 450 automobiles and 300 aircraft carriers, or 750 automobiles and 0 aircraft carriers. The right graph shows two production possibilities frontiers, one of which measures 600 automobiles and 400 aircraft carriers, and the other of which measures 800 automobiles and 400 aircraft carriers. The outward shift of the production possibilities frontier from point A to point B in the above graph would most likely be caused by