【单选题】A country produces only cans of soup and pens and it is producing at a point on its bowed out PPF. If the country increases the production of soup, the opportunity cost of an additional _________.
【简答题】O. Henry was the pen name of American writer Sydney Porter, whose sores, arc famous for their surprise endings, to the point that such an ending is often mentioned as an ‘o. Henry ending’ He was born ...