Why are quantum gates usually reversible?

Question: Why are most quantum gates reversible? A) Because they are represented by unitary transformations B) Because they destroy information during measurement C) Because they only work on classical bits D) Because they always reduce the number of qubits Correct: A Explanation: Quantum gates are generally modeled as unitary operations. A unitary operation preserves the total probability of the quantum state and has an inverse, which makes the operation reversible before measurement. Topic: quantum computing / unitary gates