In MCP, Tools are the primitive explicitly designed to be model-controlled. They represent executable functions that an MCP server exposes so that a language model can take actions, retrieve information, query databases, invoke APIs, modify files, or perform computations. The uploaded question set identifies Tools as the correct answer.

The official MCP specification defines three principal server primitives with different control models: Prompts are user-controlled , Resources are application-controlled , and Tools are model-controlled . Tools can be discovered by the model-facing application and invoked automatically according to the model's contextual interpretation of the user's request.

Resources differ because they primarily provide contextual data such as file contents or database schemas. Prompts provide reusable templates or instructions normally selected through user interaction. “Schemas” are not one of the three MCP primitives in this control hierarchy; schemas describe structures such as tool parameters rather than constituting a standalone primitive.

Therefore, A is correct.

Study Guide reference/topic: Model Context Protocol (MCP) Fundamentals — MCP primitives, Tools, Resources, Prompts, control hierarchy, and tool invocation.

===============