The statistic $(n-1)s^2/\sigma^2$ is chi-square distributed with $n-1$ degrees of freedom only if
A. the sample is normally distributed with variance equal to $s^2$
B. the population is normally distributed with variance equal to $\sigma^2$
C. the sample has a Student t-distribution with degrees of freedom equal to $n-1$
D. all of the above statements are correct

Like that of the Student t-distribution, the shape of the chi-squared distribution depends on:
A. the number of its degrees of freedom
B. whether the population is unimodal or bimodal
C. the population size
D. the population standard deviation