kramacha1979 Wrote:Since this a ,<conjunction>, don't we need the sentence after and to be a independent clause?
ah, i see what you're asking. but, no, frustratingly enough, this is not a case of "X + , + conj + Y".
basically, you are wrongly interpreting that comma as part of the structure of the overall "skeleton" of the sentence, when it in fact belongs to the appositive modifier.
i'll illustrate with a color code:
The single-family house constructed by the Yana, a Native American people who lived in what is now northern california, was conical in shape, its framework of poles overlaid with slabs of bark, either cedar or pine, and banked with dirt to a height of three to four feet.
those commas belong to the orange modifier, not to the overall structure of the sentence. if you remove the orange modifier, those commas will disappear right along with it.
in general, i don't really think that this sort of thing is tested on the gmat.
i do know that the gmat absolutely requires the comma after "Y" in the list "X, Y, and Z" -- and that this particular distinction has shown up in several official problems, much to the chagrin of students who grew up learning british english -- but that's the only one of these comma-placement issues that i've so far seen actually tested.