求翻译：In subsequent development, traditional single family ranch-style designs continued to be embraced, but new forms were also introduced: The condominium, a singlefamily attached dwelling; the triplex and fourplex, three-and four-family struchres; and prefabs, which have become significantly more popular durin the last 20 years owing to their low cost and ease of construction. The prefabs have the additional distinction of being mobile. It is not uncommon to see semi-trailers hauling these modular living units along the freeways to remote destinations. In a very real sense, this phenomena marks the cutting edge of suburbanization: a move out of the traditional suburbs and into areas that were formally是什么意思？

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