Final answer:
Southwesterly monsoons and wave action lead to the development of small islands and sand dunes through sedimentation.
Step-by-step explanation:
The combination of southwesterly monsoons and wave action leads to the development of small islands and sand dunes through a process called sedimentation. When the southwesterly monsoons bring heavy rainfall, rivers carry sediment like sand and mud downstream to the coast. The wave action then moves and shapes this sediment, depositing it along the shoreline and forming small islands or sand dunes.