please, can someone explain this to me?

Consider the joint distribution function f (I, y) of a pair of random variables X, Y defined on the same sample space. For which of the following definitions of f (to, y) are X and Y independent random variables? Assume that f {:31 y) is defined on some unspecified rectangular region, and that outside this region f (3,3,0 = 0. This allows f (as, y) to integrate to 1. {Select all that apply}