**Core Concept:** Adoptive immunity is a type of acquired immunity that occurs when immune cells (T cells and B cells) are generated in the bone marrow and then travel to peripheral lymphoid organs where they mature, proliferate, and differentiate into effector cells.

**Why the Correct Answer is Right:** The correct answer, **D**, refers to the process of immune cells (T and B cells) being generated in the bone marrow and then maturing and proliferating in peripheral lymphoid organs before performing their immune functions. This is the accurate description of adoptive immunity.

**Why Each Wrong Option is Incorrect:**

A. **B:** This is incorrect because it focuses on the activation of immune cells, which is the second phase of adaptive immunity after priming in the lymph nodes.

B. **C:** This option is incorrect as it describes the process of immune cells being generated in the thymus for T cells and bone marrow for B cells. This is an inaccurate description of adoptive immunity.

C. **A:** This answer is incorrect as it only partially describes the process of adaptive immunity, focusing on the generation of immune cells in the bone marrow and their maturation in peripheral lymphoid organs. It does not mention the subsequent activation and proliferation in these organs.

**Clinical Pearl / High-Yield Fact:** The process of adaptive immunity includes both innate and adoptive immunity, which work together to protect the body against pathogens. Understanding the correct sequence of events in adoptive immunity is essential for understanding the functioning of the immune system.