Nucleoside reverse transcriptase inhibitors (NRTIs) are a class of drugs used to treat human immunodeficiency virus (HIV). Unfortunately, a major side effect of these drugs causes people to get tired very easily, often due to a lack of energy. Which of the following choices would be the best explanation as to the cause of this drug's side effect?

(Choice A)
A
The drug may be toxic to lysosomes, organelles that enzymatically break down cellular wastes.

(Choice B)
B
The drug may be toxic to the Golgi body, an organelle that receives, modifies, and transports cellular materials.

(Choice C)
C
The drug may be toxic to mitochondria, organelles that provide a source of energy (ATP) for the cell.

(Choice D)
D
The drug may be toxic to the endoplasmic reticulum (ER), an organelle that provides a source of energy (ATP) for the cell.