Which of the following is true about the t-distribution? A.They are uni-modal and symmetric. B.Regardless of the degrees of freedom it has fatter tails than the normal model. C.As the degrees of freedom increase, the t-curve looks more and more like the normal. D.All of the above.

D. All of the above.

The t-distribution, also known as Student's t-distribution, has several key characteristics:

A. They are unimodal and symmetric: Yes, the t-distribution is unimodal, which means it has one mode or peak, and it is symmetric around its mean, much like the normal distribution.

B. Regardless of the degrees of freedom it has fatter tails than the normal model: This is also true. Fatter tails mean that the t-distribution is more prone to producing values that fall far from its mean, compared to the normal distribution. This reflects greater uncertainty or variance, which is why the t-distribution is used when estimating the mean of a normally distributed population in situations where the sample size is small and the population standard deviation is unknown.

C. As the degrees of freedom increase, the t-curve looks more and more like the normal: This is correct. The t-distribution approaches the normal distribution as the degrees of freedom increase. When the degrees of freedom are above 30, the t-distribution is very similar to the normal distribution.