In Professor Meanscore's class, the first midterm exam and the second midterm exam are weighted equally toward the final grade. With the first midterm's score on the horizontal axis, and the second midterm's score on the vertical axis, indifference curves between the two exam scores are

a.straight lines with slope 2.

b.parabola shaped.

c.straight lines with slope 1.

d.L-shaped with lines extending downward and to the left.

e.L-shaped with lines extending upward and to the right.