**Core Concept**
B and T cells are both types of lymphocytes that play crucial roles in the adaptive immune system. While they have distinct functions and characteristics, they share some common features. The question is likely asking about a characteristic or process that is common to both B and T cells.

**Why the Correct Answer is Right**
Both B cells and T cells undergo clonal selection and expansion in response to antigen presentation. This process involves the activation of antigen-specific T cells by antigen-presenting cells (APCs), which then stimulate B cells to proliferate and differentiate into antibody-secreting plasma cells. This coordinated response is essential for effective immune defense against pathogens.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because B cells and T cells have distinct surface receptors. B cells express immunoglobulin receptors (antibodies), while T cells express T cell receptors (TCRs).
* **Option B:** This option is incorrect because B cells primarily function in the humoral immune response, involving the production of antibodies, whereas T cells are involved in cell-mediated immunity.
* **Option C:** This option is incorrect because while both B and T cells can undergo apoptosis (programmed cell death), this is not a unique characteristic shared between the two cell types.

**Clinical Pearl / High-Yield Fact**
B and T cell cooperation is crucial for effective immune responses. For example, T helper cells (Th cells) assist B cells in antibody production and class switching, while cytotoxic T cells (CTLs) help eliminate infected cells.

**Correct Answer:** D. Clonal selection and expansion.