The stage of reasoning makes it possible to do simple sums but not use reversible operations. -formal operations thought beings at about age eleven and is the first time child's thinking can be said to be , and .

The stage of pre-conceptual thought is characterised by thought and operation.
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The correct answer is a. when they started making tools that will them in cultivating lands, they could raise crops and that made them attached to one place for a longer period of time. after that, they started domesticating animals and building their own permanent settlements that resemble the ones we have today.