Humans have greatly increased the level of in the atmosphere. O A. argon B. oxygen O . C. carbon dioxide O D. nitrogen

You have trained year for a marathon. in your first attempt to run a marathon, you decide that you want to complete this 26-mile race in 4-5 hours. a. what is the length of a marathon in kilometers (1mile= 1.6 kilometers). b. what would your average speed have to be to complete the race 4.5 hours? give your answer in kilometers per hour.