在我们继续之前，有一个基本要点需要澄清。

There is one ___essential point that needs to be clarified before we proceed.

理论知识与实践经验之间存在本质区别。

There is an ___essential difference between theoretical knowledge and practical experience.

这些维生素是必需营养素，无论你如何精心规划饮食，你的身体都无法自行生成。

These vitamins are ___essential nutrients that your body cannot produce on its own, no matter how carefully you plan your diet.