Correct answer is D) Humans began to farm and domesticate animals.
Explanation:
D is correct answer because around 10 000 years ago Neolithic revolution started. Until then people mostly lived as hunter and gatherers, but from this period many of them started engaging themselves in agriculture and farming.
A is not correct because people started making tool much earlier, during the stone age.
B is not correct because that also happened during the stone age.
C is not correct because letters appeared later, in the third millennium BC.
