In Death Valley National Park’s Racetrack Playa, a ﬂat, dry lakebed, are 162 rocks—some weighing less than a pound but
others almost 700 pounds—that move periodically from place to place, seemingly of their own volition. Racetrack-like trails
in the ______ mysterious migration.
playas sediment mark the rock’s
playa’s sediment mark the rocks
playa’s sediment mark the rocks’
playas’ sediment mark the rocks’
Choice C is the best answer. The convention being tested is the use of plural and possessive nouns. The singular possessive
noun “playa’s” and the plural possessive noun “rocks’” correctly indicate that the sediment is that of one playa (the Racetrack
Playa) and that there are multiple rocks that have mysteriously migrated across the sediment.
Choice A is incorrect because the context requires the singular possessive noun “playa’s” and the plural possessive noun
“rocks’,” not the plural noun “playas” and the singular possessive noun “rock’s.” Choice B is incorrect because the context
requires the plural possessive noun “rocks’,” not the plural noun “rocks.” Choice D is incorrect because the context requires
the singular possessive noun “playa’s,” not the plural possessive noun “playas’.”