Ture or False with EXPLAIN!

1) Consider a consumer's demand for a good X. If the price of a gross substitute for X goes up at the same time that the consumer's income goes up, then the consumer's demand for good X will go up as well. 2) The utility function U(x, y) = x3 + 3x y + 3xy2 + y3 is an example of preferences of perfect substitutes. 3) If preferences are complete, then either x > y or y > x 4) Preferences that can be represented by upward sloped indifference curves violate the assumption of strict convexity. 5) The condition that MRS = MRT needs to hold whenever the optimal bundle is interior. 6) The MRS for the quasilinear preferences only depends on the non-linear good in that utility function