Approximately what was the average concentration of CO2 in 1960?a. 315 ppmvb. 340 ppmvc. 300 ppmvd. 500 ppmvApproximately what was the average concentration of CO2 in 2007?a. 365 ppmvb. 340 ppmvc. 380 ppmvd. 370 ppmvBy about what percent did CO2 concentration increase between 1960 and 2007?a. 30% b. 10%c. 25%d. 20%Prior to the industrial revolution in the 1800s, the average concentration of CO2 was about 280 ppmv. By approximately what percent have CO2 concentrations increased from their pre industrial value?a. 40%b. 35%c. 25%d. 20% e. 15%