During Glacial Periods in the Early Evolution of Land Plants

During glacial periods in the early evolution of land plants, which of the following would have been a beneficial adaptation regarding the number of stomata per unit surface area, and what accounts for it?

A) increased numbers of stomata, to maximize absorption of increasing levels of atmospheric CO₂
B) increased numbers of stomata, to maximize ability to absorb low levels of atmospheric CO₂
C) decreased numbers of stomata, to retain CO₂ produced by the chloroplasts
D) decreased numbers of stomata, to maximize absorption of low levels of atmospheric CO₂