**Core Concept**
Acute auto-graft rejection is a type of immune response that occurs when the body's immune system recognizes the transplanted organ as foreign and mounts an attack against it. This process involves the activation of T cells and the production of antibodies, leading to inflammation and damage to the graft.

**Why the Correct Answer is Right**
The correct answer is related to the timing of acute auto-graft rejection. Acute rejection typically occurs within the first few months after transplantation, with the majority of episodes occurring within the first 3-6 months. This is because the immune system has not yet been fully suppressed by immunosuppressive medications, and the graft is still being recognized as foreign by the body's immune cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too broad - chronic rejection can occur at any time after transplantation, not just within a specific timeframe.
**Option B:** This option is incorrect because it is too narrow - acute rejection can occur as early as 1-2 weeks after transplantation, not just within a specific range.

**Clinical Pearl / High-Yield Fact**
Acute rejection is often triggered by an increase in the recipient's blood urea nitrogen (BUN) or creatinine levels, indicating kidney function impairment. Monitoring these levels is crucial in detecting acute rejection early, allowing for prompt intervention to prevent graft damage.

**Correct Answer: C. 3-6 months**