Which of the following has proved helpful in preserving pollen as...

Sporopollenin is helpful in preserving pollen as fossils. The covering of pollen grain, sporoderm is consist of two layers, viz., exine and intine. The exine is made of a highly resistant fatty substance called sporopollenin. It could not be degraded by an enzyme. It is not affected by high temperature, strong acid or strong alkali. Thus, it keeps the pollen grains well-preserved as fossils.
Pollenkitt is a yellowish, viscous, sticky and oily layer that covers exine of some insect-pollinated pollen grains. Intine of pollen grains is made up of pectin and cellulose.