In the Context of Romanesque Architecture, a Tympanum Refers To

In the context of Romanesque architecture, a tympanum refers to:

A) a spherical triangle that transforms a square bay into a circle for the springing of a dome.
B) a surface representing one-fourth of a sphere and often covering an apse.
C) the semicircular panel created under the arch of a doorway.
D) a large hall composed of many columns placed close together to support the roof.
E) the vault formed by two intersecting barrel vaults.