The coordinates of the endpoints of `bar(AB)` and `bar(CD)` are A(x1, y1), B(x2, y2), C(x3, y3), and D(x4, y4). Which condition proves that ` bar(AB)||bar(CD)`?

A.
`((y_4-y_2)/(x_4-x_2)= (y_3-y_1)/(x_3-x_1))`

B.
`((y_4-y_3)/(y_2-x_1)= (x_4-x_3)/(x_2-x_1))`

C.
`((y_4-y_3)/(x_4-x_3)= (y_2-y_1)/(x_2-x_1))`

D.
`((y_2-y_1)/(x_4-x_3)= (x_2-x_1)/(y_4-y_3))`