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Q. Why do you continue to support the nonpossessive apostrophe, as in CD’s, MBA’s? It serves no function whatsoever.
A. Actually, Chicago omits the apostrophe in the plurals of initialisms, while acknowledging its usefulness in some cases, particularly with the plural form of lowercase letters (e.g., x’s and o’s). (Not that punctuation is necessarily logical, you know; sometimes it is simply based on convention.)