GMAT Problem Solving Question 51: Undefined expressions

 
Try the following GMAT Problem Solving question on conditions under which algebraic expressions are undefined.

Question 51:

For what real values of $x$ is the expression $\dfrac{3(x+3)}{(x-1)(x+2)}$ not defined ?

1. $\quad x=-3 \; \textrm{only}$

2. $\quad x=-2 \; \textrm{only}$

3. $\quad x=1 \; \textrm{only}$

4. $\quad x=-2 \; \textrm{or} \; 1 \; \textrm{only}$

5. $\quad x=-3, -2, \textrm{or} \; 1 $