Final answer:
The expression 4/x - 9 is not defined when x = 0.
Step-by-step explanation:
When substituting x = 0 into the expression 4/x - 9, we get:
4/0 - 9
However, division by zero is undefined. Therefore, the expression 4/x - 9 is not defined when x = 0. So, the correct answer is D. None of the above.
Learn more about Expression evaluation here: