What defines a CSS code?

Question: What is a key feature of CSS quantum error-correcting codes? A) They require only one physical qubit per logical qubit B) They separate bit-flip and phase-flip error checks using structures derived from classical linear codes C) They forbid stabilizer measurements D) They work only for classical information Correct: B Explanation: CSS codes are a class of stabilizer codes where X-type and Z-type checks have a separated structure. This makes them useful for understanding and constructing quantum error-correcting codes. Topic: quantum computing / CSS codes / error correction