Answer:
a. always equal to zero.
Step-by-step explanation:
The mean is the sum of the values of all elements in a data-set divided by the size of the data-set.
For the sum of deviations, we sum(if positive) or subtract(if negative) all the elements with the mean.
Doing this, the result will always be 0.
Simple example:
Data set: {5,7}
Mean: 6
(5 - 6) + (7 - 6) = -1 + 1 = 0
So the correct answer is:
a. always equal to zero.