A quatrain may also be any group of four lines unified by a rhyme scheme. Quatrains usually follow an abab, abba, or abcb rhyme scheme.

四行诗通常是通过押韵组合成的四行诗节的诗，亚运形式一般为abab， abba，或abcb。

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Methods Rabbit marrow stem cells (MSCs) were cultured and expanded in vitro. The MSCs were mixed with acellular bovine cancellous bone (ABCB).

方法：体外扩增诱导兔骨髓基质干细胞，将其与去细胞牛松质骨复合培养。

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