A) The domain of this relation would be 0,4,3,5, and 6. These are our possible x values for the function. Since this equation doesn't tell us to assume that it's a function then it's fine for us to list them separately.
B) The range of this function is 2 and 1. This is for the same reasons listed in A.
C) This can be a function because although it has the same y-values several times, the x values are always different. This would not be a linear function though, since the slope should be zero, and the value (5,1) would come off of the function y=2.