adding mass to the crust causes

a. the crust to rebound
b.the mantle to rebound
c. the crust to become depressed.
d. the mantle to displace the crust.

To determine the correct answer, we need to understand the concept of isostasy in geology. Isostasy refers to the equilibrium maintained by Earth's crust and mantle, where the less dense crust floats on the denser mantle. When mass is added or removed from the crust, it affects the balance between the crust and the mantle, leading to adjustments in the topography.

When mass (such as sediment, ice, or water) is added to the crust, the answer is (c) the crust becomes depressed. The added weight causes the underlying mantle to flow away from the area of increased mass, resulting in the crust sinking or subsiding. This is known as crustal subsidence.

On the other hand, if mass is removed from the crust, such as through erosion or melting of ice, the crust rebounds or uplifts. The mantle then flows back underneath the unburdened crust, causing it to rise.

Therefore, in the given options, (c) the crust becomes depressed is the correct answer when mass is added to the crust.