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concrete – n. a hard substance used in building
implication – n. a result or effect
delta – n. a low, flat area of land where a river divides into smaller rivers and goes into the sea
alternative – n. one of two or more things to choose between
vanish – v. disappear
fortress – n. a castle or other strong building built to defend a place
foundation – n. the part of a building that sits under the ground to support it
