Question $27$

A sensor network uses a spanning tree among the sensors to aggregate temperature data up to the base station $($which is at the root of the tree$).$ The base station is interested in the average of all sensor temperature readings. So$,$ each sensor collects some $$values$$ from each of its immediate children in the tree, and communicates some values to its parent in the tree. To minimize energy consumption, we desire these values be as small as possible. Which of the following options is the best for what these values should be$?$