**Core Concept**
Carbohydrate antigens, also known as glycans, are complex molecules composed of sugar units that play a crucial role in various biological processes, including cell-cell interactions, signaling, and immune responses. These antigens can be found on cell surfaces, in extracellular matrices, and as components of pathogens, making them important targets for the immune system.

**Why the Correct Answer is Right**
Carbohydrate antigens are recognized by the immune system through specific receptors, such as the lectin-like receptors on natural killer T (NKT) cells and the C-type lectin receptors on dendritic cells. These receptors interact with carbohydrate moieties on the surface of cells or pathogens, triggering an immune response. The interaction between carbohydrate antigens and their respective receptors is a critical step in the recognition and elimination of pathogens.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is actually true, as carbohydrate antigens can be found on the surface of various cells, including tumor cells, and can serve as targets for immune cells.
**Option B:** This statement is also true, as carbohydrate antigens play a crucial role in cell-cell interactions and signaling, particularly in the context of immune responses.
**Option C:** This statement is true as well, as carbohydrate antigens can be recognized by the immune system through specific receptors, leading to an immune response.

**Clinical Pearl / High-Yield Fact**
Carbohydrate antigens are often used as targets for cancer immunotherapy, as they are frequently overexpressed on tumor cells and can be recognized by the immune system.

**Correct Answer: A**