Answer;
D. redwood tree forests.
Explanations;
Gymnosperms are seed-bearing vascular plants including, conifers, cycads, ginkgo, in which the ovules or seeds are not enclosed in an ovary.
In gymnosperms the cone is the female reproductive part and the pollen is the male reproductive part.
Red wood trees are examples of gymnosperms and are important in maintaining the balance of carbon dioxide in the atmosphere like other green plants.