Why is error correction difficult in quantum computing?

Question: Why is quantum error correction difficult? A) Classical bits cannot be stored anywhere B) Quantum states are fragile, cannot be copied perfectly, and require many physical qubits to protect logical information C) Quantum gates are always perfect D) Measurement never changes a quantum state Correct: B Explanation: Quantum error correction must protect fragile quantum information without directly copying unknown states. Practical error correction usually requires many physical qubits to encode one reliable logical qubit. Topic: quantum computing / error correction