What is the preposition of the sentence: the rider's trail began at st joseph, missouri?

(1) fire extended humans’ geographical boundaries by allowing them to travel into regions that were previously too cold to explore. (2) it also kept predators away, allowing early humans to sleep securely. (3) fire, in fact, has been a significant factor in human development and progress in many ways. (4) other obvious benefits of fire are its uses in cooking and in hunting. (5) probably even more important, however, is that learning to control fire allowed people to change the very rhythm of their lives. (6) before fire, the human daily cycle coincided with the rising and setting of the sun. (7) with fire, though, humans gained time to think and talk about the day’s events and to prepare strategies for coping with tomorrow. the sentence that expresses the main idea is: (type the number of the sentence. then click “go.”)

Why did martin luther king jr mention the ancient greek philosophersocrates in his letter

In a series of experiments, hershey and chase radioactively labeled dna and protein in viruses and then used labeled viruses to infect bacteria. hershey and chase's experiments definitively showed that a. dna and not protein is the genetic material. b. dna and protein work together as a cell's genetic material. c. protein and not dna is the genetic material. d. neither dna nor protein act as a cell's genetic material