Answer:
B. Constructive interference
Constructive interference occurs when two or more waves combine to produce a wave with a larger amplitude. In the case of identical waves, if their peaks and troughs align perfectly (they are "in phase"), the amplitude of the resultant wave is indeed doubled. This is due to the principle of superposition, which states that the displacement of a medium caused by two or more waves is the algebraic sum of the displacements caused by the individual waves.