Ed M. answered 01/06/16
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Help with grammar, French, SAT Writing, the TOEFL and ESL.
I'm not entirely sure, but I think the word agriculture would be appropriate to fill the blank in your sentence here. As I understand it, the theory is that the practice of agriculture, which by definition means growing crops usually for food, really blossomed [pardon the pun] during the Neolithic Era in human history.
One concern I have about putting agriculture in this blank is that there is a potential ambiguity in the way the sentence is constructed, that is, developed better tools and ______ could also be read to mean better tools and better ________, where the second better is actually omitted but still understood. So you'd have to be careful what you put in the blank since whatever it is it would then have to have existed before the Neolithic period (that is, like tools, humans had this before the Neolithic, but during his period they just made it better). Again, I'm no expert so I'm not sure how far back in history agriculture is thought to have existed, so there might well have been rudimentary agriculture even before the Neolithic, but to avoid this problem altogether you could simply recast your sentence as developed _______ and better tools (though if you kept the defining relative clause which means they grew their own foods you'd clearly have to put this after the blank and comma and before a new comma before and, and the result would be kind of awkward).