Subject-Verb Agreement
1.
Either the interviewer or the committee members usually begins by asking simple questions about your background.
http://grammar.ccc.commnet.edu/grammar/sv_agr.htm
Scroll down and read #5. Then let me know what you think, and I'll give you feedback.
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Based on the subject-verb agreement rule, when a compound subject is connected by "or," the verb should agree with the closer subject. In this case, the closer subject is "committee members," so the correct verb should be "begin" rather than "begins."
As per the question and the information provided, it seems that the sentence has the correct subject-verb agreement. The verb "begins" agrees with the singular subject "interviewer," even though the compound subject includes "committee members." Hence, this sentence is grammatically correct.
If you have any specific feedback or further questions, please let me know.