The thing that is used as a symbol for Mr. Craven's closed heart is D. The locked door to the secret garden.
What is Symbolism?
This refers to the literary element that makes use of objects or elements to create a significance of which something important can be linked to the object or element.
Hence, we can see that from the complete text, there is the use of narration to show that Mr Craven has a closed heart and this affects his relationship with others and this is symbolized by the locked door to the secret garden.
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