Answer the Riddle, get the points!!

Desalination is expensive because it requires

(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.”)

Me with this questions i really need them right 4. any complex sentence contains a. independent clauses only b. dependent clauses only c. one independent clause and one or more dependent clauses d. neither independent clauses nor dependent clauses 5. an appositive is a phrase or clause that a. is a noun or group of words acting as a noun b. is placed right next to a noun c. gives more information about a noun d. all of the above 6. select the correctly punctuated sentence containing appositve. a. the vocational counselor an experienced placement specialist has agreed to me get a job. b. the vocational counselor, an experienced placement specialist has agreed to me get a job. c. the vocational counselor an experienced placement specialist, has agreed to me get a job. d. the vocational counselor, an experienced placement specialist, has agreed to me get a job.