问题如下：
Based on the following information the standard error of the sample mean is closest to:
选项：
A.0.13
B.1.19
C.13.49
解释：
B is correct. population standard deviation is (128)^0.5=11.3137, so standard error =11.3137/{(90)^0.5}=1.19
老师，为什么不选C哇？已知population variance的情况下，不是应该用128除以根号90么？
