Which of the following statements about waves is/are correct? 1. Within air, waves propagate as longitudinal waves. 2. In liquids, the particles do not execute transverse oscillatory motion during wave movement. 3. Waves are never reflected when they strike an obstacle because of the dynamic nature of air. 4. On the upper surface of water, the alternate rises and falls produced by waves are called crests and troughs respectively. Select the correct answer using the code given below: