It takes place of a noun, so its a pronoun
A diagram is a noun.
If you mean what part of speech it is, then you put it under preposition.
The letter D represents a determiner on the diagram. Determiners are words that introduce and clarify nouns.
A diagram is a noun.
predicate nominative
vdfhrtegvberbht
data flow diagram for voice recognition
An indirect speech tree diagram typically branches into reported speech and reporting verb. The reported speech branch includes the actual spoken words being reported, while the reporting verb branch includes the verb used to convey that speech. The tree diagram can further branch into tenses, pronoun changes, and any other modifications required.
The part of speech for "answer" is a noun.
part of speech
The part of speech for this particular word is a noun.
adverb