I would explain, but since you had the mind to post numerous questions, I only have time to give you the answers. Sorry about that. 
1. C
2. C
3. C
4. D
5. A
<span>6. B</span>
        
             
        
        
        
Answer:
They disappeared afta the water melted 
Explanation:
 
        
                    
             
        
        
        
The correct answer to this open question is the following.
The Altithermal period changed the cultures of early American Indian peoples in Oklahoma in that higher temperatures made the weather change and grasslands spread over most of the Oklahoman territory. The eastern part of Oklahoma remained with woodlands. This grassland spread helped to attract big animals such as Buffaloes and other types of animals like rabbits, deers that could adapt to the climate conditions. Of course, this factor helped to attract Native American Indians because they could hunt those animals to feed their families. So yes, changing temperatures affected society and is a major factor to limit or attract people to one territory, depending on the highs and lows of climate conditions.
 
        
             
        
        
        
The answer to this question is: Valid
For example, let's say that a researcher wants to study the psychology of motivation as a variable.
In this case, motivation does not possess a measurable standard that could be used as data, so the researcher could only predict thte amount of motivation through the amount of job done (but this data is reliable because motivation is only on of the many factors that may influenced it)
        
             
        
        
        
Answer: have employed violence and terrorism.
- In the case of Kurdistan, most violence has come from the Kurdistan Worker's Party, a militant organization based in Turkey and Iraq. The Party has been in an armed conflict with Turkey since 1984. It is listed as a terrorist organization by NATO, the U.S., The U.K., Japan and the E.U., among others.
 - In Northern Ireland, the movement has been led by the Irish Republican Army (IRA). The IRA has been active for most of the 20th and 21st centuries, and it was dedicated to achieving Irish independence initially,  and Irish unification afterwards. The organization has been split many times over the years, and has used violence and terrorism several times over its existence.