Answer:
Because they do not have consistent data.
Explanation:
In the a case, there is a measurement (221.03 g) that is to far away from the others measurements, so this is an error that will change the result, and it needed to be measure again because is not trust value.
In the case of b and c measurements, is the opposite, the differences among one and other value is to close, in this way can be a repeated value, so there is not a significant difference, so again, the values are not trust.
Hope this info is useful.