In Several Studies of Plant Responses to Elevated CO₂ Concentrations

Multiple Choice

In several studies of plant responses to elevated CO₂ concentrations in the atmosphere,scientists often found that the stimulation of growth gradually diminished because

A) more photorespiration occurred.
B) C₃ plants were replaced with C₄ plants.
C) the soil did not contain sufficient nitrogen and other nutrients to support the enhanced growth.
D) the plants could not store the extra biomass.
E) weedy plants took over the experimental plots.