Which of the following has proved helpful in preserving pollen as fossils?

Sporopollenin is one of the most resistant organic material known. It can withstand high temperatures and strong acids and alkali. No enzyme that degrades sporopollenin is so far known. Pollen grains are well preserved as fossils because of the presence of sporopollenin.Pollen kitt helps the insects to carry out pollination in insect pollinated flowers.The inner wall of the pollen grain is called the intine. It is a thin and continuous layer made up of cellulose and pectin.Oil content has no role in preserving pollen as fossils.