夏至日的日期为________前后，太阳直射在________，北半球昼夜长短状况为________。
6.22；北回归线；昼长夜短
砌筑砂浆分为（）个强度等级。
A.10
B.8
C.6
D.4
The least accurate statement about measures of dispersion for a distribution is that the:（）
A. range provides no information about the shape of the data distribution.
B. mean absolute deviation will always be smaller than the standard deviation.
C. arithmetic average of the deviations around the mean will always be equal to one.
