
Answer:
C. He should run a T-test, and approximating it with a normal distribution would be inappropriate.
Step-by-step explanation:
We are told that the standard deviation is unknown.
Now in statistics, when we know the standard deviation, then we use a Z-test but when we don't know the standard deviation, then we will use a t-test.
Now, the t-test assumes a normal distribution for difference in mean of samples but it doesn't assume so for population.
Thus, we will run a t-test and doesn't need to approximate with a normal distribution.