**Core Concept**
Acquired immunity refers to a type of immune response that develops after exposure to an antigen, either through infection or immunization. This form of immunity involves the activation of immune cells and the production of antibodies, which provide long-term protection against future infections.

**Why the Correct Answer is Right**
Acquired immunity is characterized by the clonal expansion of antigen-specific T and B lymphocytes, which recognize and respond to specific antigens. This process involves the activation of helper T cells (Th cells), which stimulate B cells to produce antibodies and activate cytotoxic T cells (Tc cells) to kill infected cells. The production of antibodies and the activation of immune cells provide long-term immunity against future infections. This type of immunity is typically specific to the antigen that triggered the immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because innate immunity is a non-specific defense mechanism that provides immediate protection against infection, but it does not involve the activation of immune cells or the production of antibodies.
**Option B:** This option is incorrect because tolerance is a state of unresponsiveness to an antigen, which can occur through various mechanisms, including clonal deletion or anergy.
**Option C:** This option is incorrect because immunological memory is a characteristic of acquired immunity, but it is not a definition of acquired immunity itself.

**Clinical Pearl / High-Yield Fact**
It's essential to note that acquired immunity can be further divided into active and passive immunity. Active immunity occurs when the body produces its own antibodies in response to infection or immunization, while passive immunity occurs when antibodies are transferred from one individual to another through breast milk or immunoglobulin therapy.

**Correct Answer:** C.