A Sea Island is typically formed by:

• A. A tidal flat.
• B. A submerged reef.
• C. A coastal island formed by sediment deposition from the sea.
• D. A cliffed headland.

Answer: (C)

Sediment deposition from the sea building up to form land is what creates a sea island. Over time waves and currents transport and drop sand and other sediments in coastal waters, and continuous accumulation raises the surface above sea level, producing a low-lying island along the coast. This is typical of sea islands, which are usually sandy and lie near shore.

The other options don’t fit this process: a tidal flat stays intertidal and generally does not rise above water as a distinct island; a submerged reef remains underwater; a cliffed headland is raised rock carved by erosion, not formed by sediment piling up from the sea.