Which characteristic of pollen makes it a good marker in the fossil record about earth's history?

A. Pollen is only produced in certain climates and at certain elevations.

B. Pollen is identical for every plant, making it a good marker for plant life.

C. Certain pollen-producing plants grow in certain climates better than others.

D. Pollen is produced in large amounts by plants, so it's easy to find.