Amelia can produce the following combinations of A and B: 100A and 20B, 50A and 30B, or 0A and 40B. The opportunity cost of one unit of B for Amelia is
a) 5 units of X.
b) 0.2 units of X
c) 3 units of X
d) 1/2 unit of X.
e) none of the above