Try the following SAT math practice question (No Calculator) that tests your understanding of factorization and algebraic identities.

**Question**(No Calculator):

Which of the following must be a factor of both $x^4-y^4$ and $x^3y – x y^3$ ?

- $x + y$
- $x^2 – y^2$
- $(x-y)^2$

- $\quad \textrm{II only}$
- $\quad \textrm{I and II only}$
- $\quad \textrm{I and III only}$
- $\quad \textrm{I, II, and III}$