**Core Concept**
The question tests the understanding of immunological principles in organ transplantation, specifically kidney transplantation, focusing on the mechanisms of rejection and the importance of **Human Leukocyte Antigen (HLA)** matching.

**Why the Correct Answer is Right**
**Humoral immunity** and **Cell-Mediated Immunity (CMI)** are both crucial in the rejection of transplanted kidneys. Humoral immunity involves **antibodies** produced by B cells, while CMI involves T cells. **HLA** matching is critical because it reduces the risk of rejection by ensuring the donor and recipient have similar immune profiles, thus minimizing the immune response against the graft.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because humoral antibodies do play a role in rejection, particularly in acute and chronic rejection processes.
**Option B:** Incorrect as CMI is indeed responsible for rejection, with T cells recognizing the graft as foreign and initiating an immune response.
**Option D:** Incorrect because HLA identity similarity is relevant and important for reducing the risk of rejection, though the frequency of such similarity can vary.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **HLA matching** significantly improves graft survival rates by reducing the risk of immune-mediated rejection. Understanding the mechanisms of rejection, including both humoral and cellular immunity, is crucial for managing transplant patients.

**Correct Answer:** C. Donor's antibody on transfusion can cause rejection