The revision that is best to make the diagram more helpful is D. a label indicating the depth of the drainage layer.
What is a Revision?
This refers to the editing of a text to make it better by the addition of new details and the removals of errors.
Hence, we can see that when making a revision of the given diagram of a plant, the best revision that would make the diagram easier to understand would be a label indicating the depth of the drainage layer.
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https://brainly.com/question/8823021