**Core Concept**
Primary active transport is a type of transport mechanism that uses the energy from ATP hydrolysis to move molecules against their concentration gradient. This process involves the direct use of ATP to drive the transport of ions or molecules across a cell membrane, often against the concentration gradient.

**Why the Correct Answer is Right**
Primary active transport is a crucial mechanism that allows cells to maintain ion gradients, regulate pH, and transport essential nutrients. The Na+/K+-ATPase pump is a classic example of primary active transport, where the enzyme uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell against their concentration gradients. This process is essential for maintaining the resting membrane potential and regulating various cellular functions.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a clear example of primary active transport. Without more information, it's difficult to determine if this option is a correct or incorrect example.
**Option B:** This option is incorrect because it is a type of facilitated diffusion, which does not require energy to move molecules across the cell membrane.
**Option C:** This option is incorrect because it is an example of secondary active transport, where the transport of one molecule is coupled to the concentration gradient of another molecule.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that primary active transport is a critical mechanism for maintaining ion gradients and regulating pH in the body. The Na+/K+-ATPase pump is a prime example of primary active transport, and its dysfunction can lead to various clinical conditions, including hypertension and cardiac arrhythmias.

**Correct Answer: C. Sodium-potassium pump is an example of secondary active transport.**