Answer:
D
Explanation:
Mean tells us the average (in this case, total marks/ total number of students).
Standard deviation tells us the spread of a set of data from its mean (how much it deviates from the mean).
Thus, standard deviation can be used to determine the consistency of a data. The smaller the standard deviation, the more consistent the data is.
Since 4S has the smallest standard deviation of 1, it shows the most consistent achievement in the test.