Barrier islands form as the direct result of
a) precipitation
b) deposition
c) erosion
d) abrasion

The one responsible for causing barrier islands to be formed is the deposition. This is the process in which it likely happens when there is a presence of small solid particles that are being moved because of the water or wind in which comes from organisms or rocks, causing deposition or even erosion.

They both have rock surfaces

The titanic is the answer