Suppose an American Worker Can Make 20 Pairs of Shoes

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 Canada is:

A) 2 apples for each pair of shoes.
B) 2 pairs of shoes for each apple.
C) ½ apple for each pair of shoes.
D) ½ pair of shoes for every 2 apples.