4) A

The only thing that can determine whether two lines are parallel is if they have the same gradient. 

The line that crosses the two points will have the gradient:

m = (y2 – y1) / (x2 – x1) = (9 – 3) / [6 – (-3)] = 6 / 9 = 2 / 3

Using y = mx + c, the only equation in the options which has the gradient (2/3) is A. (m in option A is 2/3)