What term do sleep researchers use to designate the first three stages of sleep?

The best answer for question this would be:

Non-REM sleep

In one of the stages of sleeping, dreaming is more likely to occur in this, yet it fails to have a long lasting impression on the person, rather they will easily forget the dream that had happened.

the historians cited in the article all agree with one another about the cause of the civil war. despite coming from different backgrounds and cultures, the historians agree that slavery was the root cause of the civil war. the fact that all these historiansgenerally agree with one another makes their shared viewpoints more reliable and valid, especially because the historians have different backgrounds and all work for the well-respected institutions of howard university, clemson university, and the university of colorado.

answer; i believe the correct answer is (8) eight.