样本含量分别为n[img=~/QImg/2013-10-14-10-46-38/image010.jpg]和n[img=~/QImg/2013-10-14-10-46-38/image013.jpg]的两个小样本均数比较的t检验中,自由度等于

A、n[img=~/QImg/2013-10-14-10-46-38/image010.jpg]+n[img=~/QImg/2013-10-14-10-46-38/image013.jpg]
B、n[img=~/QImg/2013-10-14-10-46-38/image010.jpg]+n[img=~/QImg/2013-10-14-10-46-38/image013.jpg])/2
C、n[img=~/QImg/2013-10-14-10-46-38/image010.jpg]+n[img=~/QImg/2013-10-14-10-46-38/image013.jpg]-2
D、n[img=~/QImg/2013-10-14-10-46-38/image010.jpg]+n[img=~/QImg/2013-10-14-10-46-38/image013.jpg]~1
E、n[img=~/QImg/2013-10-14-10-46-38/image010.jpg]-n[img=~/QImg/2013-10-14-10-46-38/image013.jpg]