Woody plants evolve in the mid-Paleozoic Era. A. atmospheric CO2 increases B. atmospheric CO2 decreases C. There is no change in atmospheric CO2 levels.

A. atmospheric CO2 increases

Explanation:

The concentration of CO2 during the Paleozoic era was much higher than the current one, due to geographical factors, but not the chemical composition of the air, which should have been more important in increasing this gas.

The highest concentrations of CO2 during the Paleozoic era occurred during the Cambrian, approximately 7000 ppm (18 times higher than current measurements). During the Late Ordovic Period the CO2 concentration was approximately 12 times higher than the current ones, with a value of 4400 ppm. These high concentrations of CO2 favored the plants colonizing the continents and thus affecting the world climate.