Cells obtain usable energy by breaking down food molecules such as glucose during cellular respiration. The aerobic stages of respiration (the Krebs cycle and the electron transport chain) take place inside mitochondria.

Mitochondria are double-membrane organelles; the folds of the inner membrane (cristae) carry the enzymes that produce most of the cell's ATP. Because ATP is the energy currency of the cell, mitochondria are called the powerhouse of the cell.

Ribosomes make proteins, the nucleus stores the genetic material and controls cell activities, and the Golgi apparatus packages and sorts proteins and lipids. None of them is the main site of ATP production.

Mitochondria option is correct.