We see that A, B, C, and E are straight lines, but D is a parabola. The graph of a quadratic equation is a parabola, so que equation of D is y = 0.1x² (the only quadratic function of the set).
Among the straight lines, there is only one of them with a negative slope, and this is line E. The only equation that has a negative slope is y = 9 - 0.5x, so this is the equation of the line E.
Now, we see that C passes through the origin, so the y-intercept must be 0. The only linear equation that has a y-intercept equal to 0 is y = x, so this is the equation of the line C.
Additionally, B and C are parallel, so they must have the same slope. Since B has a slope of 1, the equation of B must be y = x + 2, which has a slope 1.
Finally, the equation of A is y = 2x + 2 (the only one remaining).