Sand dunes are mounds of sand that lie behind the active part of a beach and are formed over many years by wind action.
(Sand dunes; are; mounds of sand that lie behind the active part of a beach and are formed over many years by wind action) (mounds of sand; lie; behind the active part of a beach) (mounds of sand; are formed; T:over many years by wind action)
Sand dunes mounds of sand mounds of sand
are lie are formed
mounds of sand that lie behind the active part of a beach and are formed over many years by wind action
behind the active part of a beach
T:over many years by wind action