Which of the following is a linear function? an xy coordinate plane is drawn. a parabolic curve that opens down is drawn. the vertex of the curve is on the axis. an xy coordinate plane is drawn. a straight line going below the origin from the second quadrant to the fourth quadrant is drawn. an xy coordinate plane is drawn. an ellipse is drawn on the axis and partially cutting the y-axis. an xy coordinate plane is drawn. a straight line starts from the y-axis and slants down to a certain point in the first quadrant, then down again with a different slope, and then down again at another slope. all the line segments are straight lines in the first quadrant.