## Core Concept
Natural Killer (NK) cells are a type of lymphocyte that play a crucial role in the innate immune system. They are known for their ability to kill tumor cells and virus-infected cells without prior sensitization. NK cells act through a balance of activating and inhibitory signals.

## Why the Correct Answer is Right
The correct answer isn't directly provided, but we can infer that the question seeks the statement that does not accurately describe NK cells. Typically, NK cells are characterized by their:
- Ability to recognize and destroy certain tumor cells and virus-infected cells.
- Function through a balance of activating and inhibitory receptors.
- Production of cytokines like IFN-γ, which helps in immune modulation.

## Why Each Wrong Option is Incorrect
Given that the specific details of options A, B, C, and D are not provided, let's hypothetically analyze:
- **Option A:** If it states that NK cells require prior antigen exposure to be effective, this would be incorrect because NK cells are part of the innate immune response and do not require prior sensitization.
- **Option B:** If it mentions that NK cells can induce apoptosis in target cells, this would be correct as NK cells can indeed induce apoptosis in tumor cells or infected cells through mechanisms like Fas-FasL interaction or release of cytotoxins.
- **Option C:** If it suggests that NK cells are primarily involved in antibody-dependent cellular cytotoxicity (ADCC), this would be partially correct but doesn't encompass their full role. However, without specifics, it's hard to declare it incorrect outright.
- **Option D:** If it states that NK cells express MHC class I molecules on their surface, this would be correct as NK cells do express MHC class I.

## Clinical Pearl / High-Yield Fact
A key point to remember is that NK cells have **inhibitory receptors** for MHC class I molecules. When these receptors engage with MHC class I on the surface of healthy cells, they send an inhibitory signal to the NK cell, preventing it from killing the cell. This mechanism prevents NK cells from attacking normal cells.

## Correct Answer Line
**Correct Answer: D.**