A. They contain an inner and an outer membrane.

B. The region enclosed by the inner membrane is termed the matrix.

C. They contain DNA and ribosomes.

D. They are an important site for energy production in cells.

E. They contain stacked internal thylakoid membranes.

Stacked thylakoid membranes (granum), exist only in plastids, such as plant chloroplasts, not in mitochondria.