Answer: D
Step-by-step explanation:
I. Straight up false. There is no integral property that allows you to split the fractional integrand into 2 different integrals as a quotient.
II. Correct. They just used polynomial long division on the integrand.
III. Correct. They just let u=5-x, turning the limits into 1 and 3. They then rewrote it to have the order of the limits changed by multiplying the integrand by -1.