The correct word that can be used to complete the sentence is "or"
What is Concord?
This refers to the rule of grammar that notes that a subject must agree with its verb in number, etc.
Hence, we can see that based on one of the rules of concord, because the word "either" is used, this means this or that, and therefore, the word "or" is used to complete it.
Read more about subject-verb agreement here:
https://brainly.com/question/1835508
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