Answer the following question given this paragraph: 

In stage two, the pyruvate molecules are transported into the mitochondria. The mitochondria are the organelles known as the energy "powerhouses" of the cells ( Figure below ). In the mitochondria, the pyruvate, which have been converted into a 2-carbon molecule, enter the Krebs cycle. Notice that mitochondria have an inner membrane with many folds, called cristae . These cristae greatly increase the membrane surface area where many of the cellular respiration reactions take place.


Q: What organelles are known as the energy "powerhouses" of the cells?

 Choices:

- proteins

- atoms

- carbohydrates

- mitochondria

A:
mitochondria
