Answer: Conservation concept is not understood by Mark
Explanation: According to the theory of Piaget, conservation is the development stage of a child where he tends to understand that even if the object changes the shape , it does not change the amount or volume of that object.
As per the case mentioned in the question, Mark lacks the understanding of conservation concept .Thus, he is not able to analyze that Tia's clay amount is equal to his own clay amount and Tia has just rolled the clay to make it longer.