**Core Concept**
Carbon monoxide (CO) is a toxic gas that inhibits cellular respiration by binding to a critical component of the electron transport chain. This binding disrupts the normal flow of electrons, leading to cellular hypoxia and tissue damage.

**Why the Correct Answer is Right**
CO binds to **cytochrome c oxidase**, also known as Complex IV, which is the terminal enzyme of the electron transport chain. By binding to the iron-heme group of cytochrome c oxidase, CO prevents the transfer of electrons to oxygen, effectively halting the electron transport chain and leading to cellular hypoxia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This component is not directly involved in the electron transport chain.
* **Option B:** While NADH dehydrogenase (Complex I) is a critical component of the electron transport chain, it is not the primary site of CO toxicity.
* **Option D:** Cytochrome b-c1 complex (Complex III) is also part of the electron transport chain, but it is not the primary target of CO.

**Clinical Pearl / High-Yield Fact**
CO poisoning is a significant clinical concern, particularly in settings with poor ventilation, such as enclosed spaces or areas with faulty heating systems. The characteristic cherry-red discoloration of the skin and mucous membranes is a classic sign of CO poisoning.

**Correct Answer: C. Cytochrome c oxidase**