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Correct answer: B. The client launches the server as a subprocess and talks to it over the standard streams.
Explanation
The principle — On this transport the client is the parent process, and everything else follows from that.
Why the key is correct — In the stdio transport, the client launches the MCP server as a subprocess. What that buys is stated too: stdio transport: uses standard input/output streams for direct process communication between local processes on the same machine, providing optimal performance with no network overhead.
Why the others are wrong — Nothing is discovered, no port is bound, and no person is typing.
Remember this — The client starts the process and speaks to it down its own streams.
Sources — MCP first-party documentation.
Sources
“In the stdio transport, the client launches the MCP server as a subprocess.”
“Stdio transport: Uses standard input/output streams for direct process communication between local processes on the same machine, providing optimal performance with no network overhead.”
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