Ok, DNA Polymerase is an enzyme that joins free nucleotides to both existing strands of DNA, which means it isn't D (which is helicase, by the way). They normally work in pairs of two for this function, so it isn't C; this is because if it created a fork, there would only be one needed. Now, concerning A & B, you'll have to be careful. Depending on how A is worded contextually, it could be correct, or it could not. I'm not sure I like the wording "chunks." Which is why I think it's B. Polymerase joins one strand of the "unzipped" DNA to free nucleotides that match it, and these aren't "chunks of DNA." Now, Polymerase is VERY accurate, only making a mistake once every millionth (or billionth?) nucleotide matchup. When it does make a mistake (most of the time), it'll go back and fix it. So I believe the best answer is B, it checks for errors.
Hope this helps!
