Respuesta :
Even though I feel like some your question is missing I would go with "WHO" because that is a relative pronoun to your sentence.
The appropriate relative pronoun in the sentence will be "who". This is explained below.
What is a pronoun?
A pronoun simply means a word that can be used to replace the noun that's in a sentence. Examples include he, she, it, etc.
Here, who is the appropriate word. The sentence will be "the teacher who began the campaign received a great deal of support".
Learn more about pronouns on:
https://brainly.com/question/870477
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