Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMAR
but that would slightly alter the implied relationships.
• Another exception is when the elements are preceded by the
pronoun each or every, which then becomes the subject. These
pronouns are treated as singulars, even in combination.
The invoice and purchase order have to be approved by the manager.
But:
Each invoice and purchase order has to be approved.
Every invoice and purchase order has to be approved.
Each of the invoices and purchase orders has to be approved.
Every one of the invoices and purchase orders has to be approved.
Each and every invoice and purchase order has to be approved.
Note: If each follows a compound subject rather than precedes
it, the verb is plural. (No one ever said English was logical.)
The invoice and purchase order (or the invoices and purchase orders)
each have to be approved.
ALTERNATIVE SUBJECTS
When two subjects that share a verb are linked by or, nor or but,
the verb agrees with whichever part is closest to it.
The carpets or the chairs are giving off a musty smell.
[both parts are plural, so verb is plural]
Either Zeke or his sister~ going to attend.
[both parts are singular, so verb is singular]
Either Zeke or his parents are going to attend.
[parents is plural, so verb is plural]
Either Zeke's parents or his sister~ going to attend.
[sister is singular, so verb is singular]
One or the other of you has to compromise.
Neither the gloves nor the scarf needs washing.
Neither the moon nor the stars were visible.
Not the weather but the bus schedules make it difficult for her to come.
Not his looks but his manner turns me off.
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