When a child can simultaneously manipulate two dimensions cognitively, such as circumference and thickness, so that s/he understands that a change in one dimension is compensated for by a change in the other, s/he understands?

The correct answer is reciprocity. Reciprocity is being defined as a practice of being able to exchange things with others for the purpose of privileges or mutual benefit by which can be granted by another party, organization or the country.

answer; ///self- learning;

answer; a biased sample;