A Number of Studies Have Found That for Many Plants

A number of studies have found that for many plants there is an increase in seed production under conditions of elevated carbon dioxide levels. What is a likely explanation for this phenomenon?

A) The energy needed to produce seeds comes from carbon dioxide.
B) The carbon needed to produce new plant molecules through photosynthesis requires carbon dioxide.
C) Increased carbon dioxide levels cause increased cell respiration, which is needed to produce more seeds.