Two singular subjects connected by either/or or neither/nor require a singular verb as in,
1)Neither John nor Susan is available.
2)Either Kiana or Casey helps today with stage decorations.
When a singular subject is connected by or or nor to a plural subject, put the plural subject last and use a plural verb.
Example The book or the magazines are on the shelf
for more details refer to link: http://www.grammarbook.com/grammar/subjectVerbAgree.asp
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