Concept:When two identical waves meet in phase, they undergo constructive interference and their displacements add up.Explanation:At point I, the two waves overlap and superpose.The resultant displacement is the sum of the individual displacements of the two waves.Each wave has amplitude A.Since the waves are in phase at I, their displacements add directly.So, the vertical displacement of the resulting wave is:A+A=2A.Answer:D. 2A
