Which of the following statements about the standard normal -distribution and t-distribution is correct? O a. The z-distribution has a spread (width) that does not depend on the sample size and the t-distribution has a spread (width) that will decrease when the sample size increases O b. The z-distribution has a wider spread (width) than the t-distribution O c. The -distribution is bell-shaped and symmetric and the t-distribution can be either left or right skewed O d. The z-distribution is centered at 0 and the t-distribution is centered at (n - 1)

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