Which of the following correctly shows the first step when factoring 3wx + 3wy - 4zx - 4zy by grouping? (Please show simple or advance explanations - 35 points is rewarded :>)

A) 3w(x + y) - 4z(x + y)
B) 3w(x + y) + 4z(x - y)
C) 3w(x + y) + 4z(x + y)
D) w(3x + 3y) - z(4x + 4y)