Why Would Sand Be Deposited Behind a Small Island to Form

Why would sand be deposited behind a small island to form a spit or tombolo?

A) The onshore current from one direction piles up sand here.
B) Waves refract around the island and the wave energy is dissipated on the island, allowing quiescent water behind, and sand drift to accumulate behind the island.
C) The island protects the coast from rip currents, preserving the sand.
D) The tidal affects are trivial behind the island, so the sand is not swept away.