Given two variables x and y, how do you test whether exactly one of them is zero? Select one: a. if x == 0 or y == 0 : b. if x == 0 and y != 0 or y == 0 and x != 0 : c. if x == 0 and y != 0 and y == 0 and x != 0 : d. if x = 0 or y = 0 :