Barrier islands:
a. Are eroded by strong wave action on their seaward side, thus moving them landward.
b. Are long, low narrow, coast-parallel, sandy islands typically less than a meter or two above sea level.

b. Are long, low narrow, coast-parallel, sandy islands typically less than a meter or two above sea level.

Explanation:

The barrier islands are those islands that are formed by the coastal erosion and are a type of a dune system that has a flat or lump area of sand and is formed by the waves and the tidal actions and are subject to change during the storms and other actions. The barriers islands are formed by the several components parts as the foreshore and the backshore  and the dunes and the tidal flats and their process of formation starts with a certain width like the outwash and the washover deposits and is a process that continues for about 150 years. And consists of the major theories of the formation related to the offshore bar, the spit accretion, and the submergence.

C. naturally in the environment