Please explain how you get the answer to this question

In Professor Meanscore's class, the first and second midterm exams 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.L-Shaped- with lines extending upward and to the right.

b.L-Shaped- with lines extending downward and to the left.

c.Parabola shaped.

d.Straight lines with slope of 21

e.Straight lines with slope of 2