The process by which an organism constantly maintains its internal body conditions, despite of varying external environmental conditions is called homeostasis. Reproduction is of two types, asexual and sexual reproduction. In asexual reproduction, a new cell is formed from a single parent. Sexual reproduction involves the production of first cell of new organism by the union of two cells from two different parents. In the process of development, new cells are formed in the same organism from the pre existing cells.
Hence, the correct answer is option (d) sexual reproduction.