The karst topography is formed by the actions of

Ground water

Explanation:

Karst topography is formed when the underground water breaks down the bedrock into soluble rocks. Hence, the bedrock of Karst topography is made of soluble rocks such as limestone. There is no surface water and topsoil in this topography and hence, the water from rains become part of the groundwater.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.

the answer is cell division : )