Why have most attempts at instituting sustainable farming practices failed?

In stage 2 farmers used the land primarily to grow food for their families and their small communities.

The difference(s) between the grand canyon and valles marineris is/are: (a) the grand canyon was formed by water, but valles marineris was not. (a) valles marineris is much longer than the grand canyon. (c) valles marineris is much wider than the grand canyon. (d) valles marineris has large volcanoes near it. all of the above

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