A nation can produce two products: smarties and wireless headphones. The table below is the nation's production possibilities schedule: Product A B C D E F Smarties 0 1 2 3 4 5 Wireless Headphone 100 90 75 55 30 0 Refer to the above table. The opportunity cost of the second unit of smarties is: 25 units of wireless headphones 12.5 units of wireless headphones 15 units of wireless headphones 20 units of wireless headphones