Correct answer: A. All things are momentary
Explanation: Kshanikavada, or the doctrine of momentariness, is an important Buddhist philosophical idea. It states that all conditioned things are temporary and arise, change, and perish from moment to moment. Nothing in the changing world possesses permanent, unchanging existence. This idea is closely connected with the Buddhist principle of anitya, or impermanence, and helps explain why attachment produces suffering. Therefore, option A is correct because it expresses the universal momentary nature of things. Option B concerns kingship, option C concerns taxation, and option D concerns social classification; none states the Buddhist doctrine of momentariness.