Answer: Option (A)
Explanation: Isostacy is considered to be the state of gravitational balance between the lithospheric crust and the rocks of asthenosphere.
When materials are added to the crust, the weight increases and the block goes down. Whereas the materials when gets erode, weight of the block decreases and subsequently rises up.
This state of balancing the crustal rocks flowing over the rocks of asthenosphere layer is known as the Isostacy.