关于模式分解，有下述说法：  

①若要求分解保持函数依赖，那么分解后的关系模式总可以达到3NF，但不一定能达到BCNF。  

②若要求分解既保持函数依赖又具有无损连接性，则可以达到3NF，但不一定能达到 BCNF。  

③若要求分解具有无损连接性，那么一定可以达到4NF。

其中，正确的说法有(30)。

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