Two functions are defined on xy plane for any arbit point(x, y) where x, y, a, b are positive. Given, f(x, y) = (ax, y) and g(x, y) = (x, by). If the quadrilateral formed by (3, 4), f(3, 4), (5, 6) and g(5, 6) is convex then which among the following is true?

1) If b > 1, then a < 5/3
2) If a > 5/3, then b > 2/3
3) If 1 < a < 5/3 then b < 2/3
4) At least two of the above