Barrier Reefs are described as:

• A. A barrier reef lies very close to shore.
• B. A coral reef that runs parallel to a coastline, separated from shore by a channel.
• C. An underwater mountain.
• D. A submerged sandbank.

Answer: (B)

A barrier reef is a coral reef that runs parallel to a coastline and is separated from the shore by a channel or a lagoon. This offshore, lagoon-separated form distinguishes it from reefs that sit right against the land. The barrier reef sits out from the shore with deeper water between the reef and the coast, which creates that wide, protected lagoon area behind the reef and a distinct offshore belt of reef.

The other descriptions don’t fit because a reef that lies very close to shore is characteristic of a fringing reef, not a barrier reef. An underwater mountain describes a seamount, not a reef structure. A submerged sandbank is a sandy feature, not a coral reef.