Answer: B. seriation
Explanation: -The ability to pass conservation tasks provides clear evidence of operations- mental actions that obey logical rules
-Capable of Decentration: focusing on several aspects of a problem and relating them, rather than centering on just one.
-Capable of Reversibility: the capacity to think through a series of steps and then mentally reverse direction, returning to the starting point
-Reversibility is solidly achieved in middle childhood