Answer:
The next period, the time of Early Specialized Hunters, refers to our earliest well-documented inhabitants, known in the literature as the "Clovis and Folsom cultures." Clovis people occupied Oklahoma around 11,000 to 12,000 years ago, and Folsom occurred somewhat later, around 10,000 years ago
Some factors that may make it difficult to keep speed during a stairway evacuation are exhaustion or the person's mental state. During a period of evacuation, the stress suffered is going to affect how people are going to respond, and how they are going to react. Also, the architecture of the stairway may affect the stairway evacuation process.
Marginal costs. Keep in mind that marginal means on the edge of something, so the cost of producing one more unit would be on the edge. Hope this explanation helps.
