When Thurston Catches 10 Fish a Day, He Can Gather

Multiple Choice

When Thurston catches 10 fish a day, he can gather a maximum of 40 coconuts, and when he catches 20 fish a day, he can gather a maximum of 30 coconuts. If Thurston's opportunity cost of producing each good increases as he produces more of it, and he decides to catch 30 fish a day, then the maximum number of coconuts he can gather must be:

A) equal to 20.
B) greater than 20.
C) greater than 10.
D) less than 20.