Atmospheric Carbon Dioxide Levels Are Shown Below

Multiple Choice

Atmospheric carbon dioxide levels are shown below.This graph was developed by measurements that were obtained by

A) direct measurements on Mauna Loa,Hawaii,and from air bubbles trapped in ice.
B) studies of the tissues of plants and their structures in response to differing CO₂ levels.
C) carbon isotope levels in sea floor sediments.
D) measurements from undisturbed bat droppings in caves on a South Pacific island.