It's d) 4x-9y....
if we take x = 10, y = 2, then 4x -9y = 22 which is divisible by 11,
if we take x = 14, y = 5 then both 3x + 7y and 4x - 9y are divisible by 11.
if we take x = 18, y = 8, then also both 3x + 7y and 4x - 9y are divisible by 11.
so i think it is D.