问题如下图：
选项：
A. 
B. 
C. 
解释：
请问B中的说法为什么是对的，T分布只由degrees of freedom就可以决定吗？是如何决定的？ 谢谢
NO.PZ2015120604000123 问题如下 Whiof the following is most likely to true for t-stribution? A.the sample size gets larger, the t-stribution approaches the normstribution. B.The grees of freem is equto n. C.The stribution is symmetry but more peaketha stanrnormstribution. A is correct.B is incorrebecause the grees of freem is equto n-1.C is incorrebecause t-stribution is less the petha stanrnormstribution.在t分布中，自由度为n-1；并且t分布的图相比正态分布要扁一些，所以B C描述错误；而A为正确描述。 自由度的作用是什么？
NO.PZ2015120604000123问题如下Whiof the following is most likely to true for t-stribution?A.the sample size gets larger, the t-stribution approaches the normstribution. B.The grees of freem is equto n.C.The stribution is symmetry but more peaketha stanrnormstribution. A is correct.B is incorrebecause the grees of freem is equto n-1.C is incorrebecause t-stribution is less the petha stanrnormstribution.在t分布中，自由度为n-1；并且t分布的图相比正态分布要扁一些，所以B C描述错误；而A为正确描述。 不是只有变化，才会影响她的形态吗，更接近正态分布吗
T分布不也是正态分布嘛，只是不是标准正态分布？为什么A不对呢
虽然知道B.C肯定是对的，请问A是不是也有道理呢？越精确也就意味着方差越小？
