Monroe Consumes Crab Cakes and Tuna

Monroe consumes crab cakes and tuna. Monroe's utility increases with the consumption of crab cakes, but his utility neither increases nor decreases with the consumption of tuna. Assuming tuna is on the x-axis and crab cake is on the y-axis, what do Monroe's indifference curves look like?

A) horizontal lines
B) vertical lines
C) upward-sloping lines from the origin
D) downward-sloping lines