What Did Piaget Mean by the Term Conservation

What did Piaget mean by the term conservation?

A) Creating a reservoir of water to ensure that there is sufficient water to supply the inhabitants of cities with all that they need
B) Failing to understand that an underlying property remains invariant despite changes in appearance
C) Preserving the natural resources of the earth such that future generations will have enough food, water, and materials to sustain civilization as we know it
D) Understanding that an underlying property remains invariant despite changes in appearance
E) Protecting rain forests against encroaching deforestation for the purpose of agriculture and building housing developments