Two different sets of one hundred plants were grown for three weeks in an airtight greenhouse at 85°F and 5% humidity. Plant set I was Zea mays, and plant set II was Abutilon theophrasti. The plants were given the same amounts of water and fertilizer, and they were grown in the same type of soil with identical illumination. The plants were grown in an environment with 405 ppm CO2. The relative growth rate of each set of plants was recorded. Plant set I grew twice as fast as plant set II. From a molecular standpoint, what is the best explanation for the enhanced growth rate of plant set I?

Plant set I has an additional metabolic pathway for capturing CO2.
Plant set I has a metabolic pathway that increases the rate of photorespiration.
Plant set I has a metabolic pathway that closes stomata during the day, which deprives the plant of oxygen.
Plant set I has an alternate metabolic pathway for capturing sunlight, which increases the rate of photosynthesis.