Explain how the limestone caves at carlsbad cavern were formed

The limestone caves at Carlsbad Cavern were formed by hydrogen-sulfide-rich (H2S) waters. This water moved through fractures and faults in the limestone and mixed with rainwater along the way. The mixture gave rise to a substance known as sulfuric acid (H2SO4). Sulfuric acid is able to dissolve limestone, eventually creating Carlsbad Cavern. The process of cave formation ended roughly four million years ago.

because the center-south is called the heart of the country

the correct answer is c.