The correct answer is: C. 6000 B.C.
Rice was first domesticated in India around 6000 B.C. This is based on evidence from the site of Koldhiwa in the Belan Valley. At this site, archaeologists have found rice grains that have been carbon dated to this period. This evidence suggests that rice was first domesticated in India, and then spread to other parts of Asia.
The other options are incorrect because they are not supported by the evidence. Option A is incorrect because it is too early. Option B is incorrect because it is too late. Option D is incorrect because it is not supported by the evidence.
The evidence from Koldhiwa in the Belan Valley is significant because it provides the earliest evidence of rice domestication. This evidence suggests that rice was first domesticated in India, and then spread to other parts of Asia. This is an important discovery because it helps us to understand the history of agriculture and the development of human societies.