Suppose an American worker can make 20 pairs of shoes or grow 100 apples per day. On the other hand, a Canadian worker can produce 10 pairs of shoes or grow 20 apples per day. The opportunity cost for the United States is:

A. 5 apples for each pair of shoes.
B. 5 pairs of shoes for each apple.
C. 1/5 apple for each pair of shoes.
D. 1 pair of shoes for every 2 apples.

A. 5 apples for each pair of shoes.