"B or C, but not A or D"---and the answer was ELEM, short for ELEMENT. B is the symbol for boron and C is the symbol for carbon. I know more about music than I know about elements. After I had the LE filled in, I thought the answer was CLEF. Nice try, Steve.
Another answer was MDII ("Year Columbus began his fourth voyage"). Yesterday's puzzle included MMIV ("Year President Bush was re-elected"). Roman numerals are appearing far too often in crosswords. Occasionally there are puzzles that use actual numbers and those puzzles are usually pretty creative. I don't live in Rome and I don't want to see Roman numerals in crosswords. I'll say this a M times if I have to!