In the table below, place each of the following item a to l in the correct box (notice that each item can be placed in ONLY ONE BOX).
a. Congested toll roads
b. Knowledge
c. Fish in the ocean
d. National defense
e. Congested nontoll roads
f. Cable TV
g. The environment
h. Fire protection
i. Ice-cream cones
j. Uncongested toll roads
k. Clothing
l. Uncongested nontoll roads