求翻译：“城市群”（城市圈）为中国大陆地区自1990年代以后常用的地域经济用语，中国大陆主要有四大城市群。本文就四大城市群及其中心城市的状况进行分析说明。是什么意思？

"Urban agglomerations" (City Circle) in mainland China since the 1990s the common geographical and economic terms, the Chinese mainland, there are four main urban agglomerations. The analysis shows that four urban agglomerations and central city status.

"Urban Clusters" (city) in mainland China since 1990s and beyond the geographical economic terms commonly used in mainland China there are 4 major cities. This article on 4 major cities and urban centers in the State.

“The urban cluster” (city circle) will be mainland China area from 1990 ages later the commonly used region economical terminology, mainland China mainly has four big urban clusters.This article carries on analysis showing on four big urban clusters and the key city conditions.

"Urban agglomeration" (cities) in the Mainland of China since 1990, common regional economic terms, there are four major cities in mainland China. This analysis shows the status of the four urban agglomeration and the central city.

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