Clark Enjoys Fishing and Hunting

Clark enjoys fishing and hunting. He divides his leisure hours between the two outdoor activities. Suppose we were to draw Clark's indifference curves for the two activities, placing fishing on the horizontal axis and hunting on the vertical axis. If Clark's indifference curves are bowed inward, then

A) the rate at which he is willing to give up an hour of hunting for an hour of fishing changes depending on how many hours of each activity he has done. For example, if Clark has already fished a lot in one week, he will be more willing to give up an hour of fishing for an hour of hunting than if he has only fished a little that week.
B) the rate at which he is willing to give up an hour of hunting for an hour of fishing is constant because he must derive the same enjoyment out of each activity.
C) the rate at which he is willing to give up an hour of hunting for an hour of fishing changes depending on how many hours of each activity he has done. For example, if Clark has already fished a lot in one week, he will be less willing to give up an hour of fishing for an hour of hunting than if he has only fished a little that week.
D) Clark's indifference curves will not cross. When indifference curves are bowed outward, the indifference curves must cross.