Sinkholes can form when

A rainwater containing carbon dioxide dissolves underground rock

Explanation:

Water in an underground rock is groundwater. Underground water can also erode and deposit material. Rainwater absorbs carbon dioxide (CO2) as it falls down to the surface. The CO2 groundwater creates landforms by getting rid of rock.

phylogenetic tree is the tree of life or evolution tree. it shows the different branches of evolution. the sequence goes like tissues - coelom - backbone - endoskeleton - segmentation

answer; i believe its (ovulation);