Digital SAT Reading and Writing Practice Question #281

Paleoclimatologists routinely use pollen preserved in ancient sediment cores to reconstruct historical ecosystems. However, pollen preservation and dispersal are highly variable across species. For example, the tough exine shell of pine pollen allows it to travel vast distances on the wind and persist for millennia in aquatic environments. Conversely, the more fragile pollen of the angiosperm *Populus* (aspen) degrades rapidly when submerged in water. In a sediment core from a freshwater lake dating to 10,000 years ago, researchers cataloged immense quantities of pine pollen but discovered virtually zero *Populus* pollen. Yet, abundant *Populus* macrofossils—such as leaves and heavy twigs, which are physically incapable of traveling far from their source tree—were successfully excavated from the exact same sedimentary layer. Which choice most logically completes the text?