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It avoids the comma-splice error of the other options by turning the first independent clause, “This basic document is stating the liberties” into an appositive. An appositive is asubordinate noun phrase that renames a noun. In this revision, “A basic document” is the appositive that renames “Magna Carta,” and the dependent clause “that states the liberties” modifies “a basic document.”
I'm also thinking more attention should be paid to teaching young children the terminology of arithmetic: addends, subtrahends, factors, and the like. I think -- I don't know -- that fluency with the terminology might help reduce associative interference. "All math looks alike": the 5 and the 2 in 5+2 look exactly like the 5 and the 2 in 5x2. But the words addend and factor have nothing in common whatsoever.
