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))`