An accretionary prism of sediments and oceanic crust is formed:

A) an oceanic trench created by the subduction of one oceanic plate beneath another plate
B) in the asthenosphere as the subduction of one oceanic plate enters the asthenosphere
C) on top of the oceanic plate that is not being subducted

Accretionary Prism

A prism- or wedge-shaped, structurally complex zone of faults, folds, and mostly metamorphosed rocks that form along the upper parts of a subduction zone; material derived from sediment contributed by adjacent volcanoes or a continent, along with oceanic crust scraped off the downgoing slab.

Oceanic Trench

Deep, narrow depressions in the ocean floor, often associated with subduction zones where one tectonic plate is diving beneath another.

Oceanic Crust

The part of Earth's crust that constitutes the ocean basins, thinner and denser than continental crust.