Final answer:
The correct answer is option A. True.The t-distribution must be used when the sample size is greater than 30 and the variable is normally or approximately normally distributed.
Step-by-step explanation:
The t-distribution must be used when the sample size is greater than 30 and the variable is normally or approximately normally distributed.
The t-distribution is used when the sample size is small and the population standard deviation is unknown. It is similar to the standard normal distribution, but has heavier tails.
When the sample size is large, greater than 30, the central limit theorem states that the sampling distribution of the means becomes approximately normal. Therefore, in this case, the normal distribution can be used as an approximation instead of the t-distribution.