A. neither/nor ;either/or; not only/but also follow the proximity rule: 5) Either the President or the three senators are going to speak …. 6) Either the three senators or the President is going to speak … (https://magoosh.com/gmat/2014/compound-subjects-additive-phrases/) B.Neither is always singular: Neither of them is... https://magoosh.com/gmat/2013/gmat-sentence-correction-indefinite-pronouns-and-agreement/ C.'None' depends on what the subject is(described in same link above) None of the students are.. None of the milk is....