I think the presence of "and/or" with its logical complications is meaningless here, and I would choose 2 and 4, thus the plural, based on the proximity of the verb to one of the pronouns (they) . Curious about opinions from other takers EDIT: now that I see your other messages, I think the proximity might not work everywhere, because I like the plural in all 3 of your messages.
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Marius HancuI think the presence of "and/or" with its logical complications is meaningless here, and I would choose 2 and 4, thus the plural, based on the proximity of the verb to one of the pronouns (they).
Curious about opinions from other takers