It is C, the cell membrane. The membrane is responsible for controlling what goes in and out of the cell by using diffusion and osmosis. The cell wall's purpose is to give shape to the cell, so the answer is C.
The cell is a logical entity: it is a compartmentalized compartment by a cell membrane (or cytoplasmic membrane) in which are grouped all the living molecules (organelles and nutrients). Without this membrane these biomolecules would be diluted in the surrounding environment.
It is the cycle when the reproductive organs start to fertilize. Another form of this is called the menstural cycle when natural changes in the uterus and ovaries to make reproduction possible soon.
