Age structure diagrams Oshow the number of males and females in the reproductive age categories. show only two age groups: reproductive and not reproductive. are strictly for present use and do not provide insight into future trends. are useful for studying developing countries but not developed countries. Question 24 (2 points) Which of the following is a method upon which historical CO2 levels are measured? examination of tree rings. Ocoring of stony corals. Ocoring of ancient ice sheets. examination of stomata on fossils of plants. all are ways in which historical CO2 levels can be estimated