The reasons fall into two main groups.

原因主要有两类。

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The dicotyledons diverged at an early stage of their evolution into two main groups.

双子叶植物在演化的早期阶段就已分化为两大支派。

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The dicotyledons diverged at an early stage of their evolution into two main groups.

双子叶植物在演化的早期阶段就已分化为两大支派。

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