Answer:
Cardona concluded that the study shows how, over the more than 25,000 years that modern humans been lived in Siberia, various peoples have adapted to the region's cold weather and meaty food sources through selection on multiple genes that control several biological mechanisms.
Explanation:
The more people that are migrating to urban areas (urbanization) needs more crops for the citizens which causes more people to grow crops and without crop rotating or methods to prevent soil degradation. More likely answer is that more industry grows in the urbanized areas and they have poor management of the soil which causes soil degradation<span />
Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by groundwater circulating through them. As the rock dissolves, spaces and caverns develop underground.
Sinkholes are formed when the land surface above collapses or sinks into the cavities or when surface material is carried downward into the voids. Drought, along with resulting high groundwater withdrawals, can make conditions favorable for sinkholes to form.
I think that a) is chemical, and b) would be chemical
