In this paper, we refine and substantiate an initial observation that different styles of conceptual physics questions (i.e., questions that ask students to explain a phenomenon versus questions that ask students to predict an outcome and explain their reasoning) elicit different kinds of conceptual resources in students' responses. We analyze the responses that students from three universities gave to written questions about reflection of mechanical pulses. Some responses draw on rules, principles, or procedures; other responses use ideas about force, energy, and motion to reason about wave phenomena. In this preliminary study, we investigate the frequency of each kind of response. We find that a question which asks students to predict the outcome of an experiment regarding mechanical wave reflection more commonly elicits ideas about rules, principles, and procedures, while a question that describes the outcome of a wave propagation experiment and asks students to explain the phenomenon more commonly elicits ideas about forces, energy, and motion.