Key concept: A rational expression (aka fraction) is undefined when the denominator equal zero

So let's check each denominator individually and see what values of x make that denominator equal to zero.

If $x^2 - 1 = 0$, then $x^2 = 1$, which means $x=1$ and $x=-1$
In other words, the expression is not defined when $x=1$ and when $x=-1$

If $x^2 - 4x + 4 = 0$, then we can factor the left side to get: $(x-2)(x-2)= 0$
This means $x = 2$
So, the expression is not defined when $x=2$

So the expression is undefined when $x=1$, $x=-1$ and $x=2$

Answer: E

Cheers,
Brent