The answer is D it's made of different kinds of tissues,due to the fact most animals and plants have organs,which are self-contained groups of tissues(more than one) such as the heart that work together to perform one function.
Some of the major factors which affect the genetic equilibrium and induce the variability in population are as follows: (A) Mutations (B) Recombinations during Sexual Reproduction (C) Genetic Drift (D) Gene Migration (Gene Flow) (E) Natural Selection.