Explain why the Xia dynasty is usually not considered to be the first dynasty in ancient Chinese history.

The Xia Dynasty is so old that it is still not certain whether or not the dynasty actually existed. It is believed to have been started by Yu the Great around 2070 B.C., but as a result of how early this is, it is difficult to determine whether it existed.

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a factory opens that mass-produces light bulbs.

explanation:

not sure if that's an answer to your questions but this is an example! : )