The correct relative pronoun is A. Who.
This refers to the type of pronoun that is used to show the relation between one person or thing and another.
Hence, we can see that from the given sentence, there is the mention of a person that kicked off a conference and how he was a dull person and the relative pronoun that best completes it is option A.
Read more about relative pronouns here:
https://brainly.com/question/955835
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