The best answer is A.
Mitochondria are small organelles found floating free in the cytoplasm of both animal and plant cells. They consist of two membranes, an outer and inner membrane which has numerous folds creating layered structures called cristae.Inside the mitochondria, there is found fluid called the matrix
Mitochondria are the powerhouse of cells. Many of the reactions in cellular respiration that take place in the cell occur in mitochondria and thus these organelles are key in the production of energy .