Diagram illustrates wave bending around obstacles

Steps:

• Identify key visual: Waves pass through a gap or around barrier and spread out.
• Recall diffraction definition: Bending and spreading of waves when encountering an obstacle or aperture comparable to wavelength.
• Match diagram to behavior: Spreading pattern indicates diffraction, not straight propagation.
• Rule out alternatives: No frequency change, no pattern of reinforcement/destruction, no simple overlap.

Why A is correct:

• Diffraction occurs when waves encounter an edge or slit, causing them to bend and interfere, producing curved wavefronts as per Huygens' principle.

Why the others are wrong:

• B: Doppler shift involves frequency change due to relative motion, absent in static diagram.
• C: Interference requires overlapping waves creating bright/dark fringes, not shown as bending.
• D: Superposition is the principle of wave addition, but diagram shows specific bending, not general overlap.

Final answer: A