TASK DEFINITION: In this task you are given a sentence. You must judge whether subject of the main clause is singular or plural. Label the instances as "Singular" or "Plural" based on your judgment.
PROBLEM: But her efforts seemed futile.

SOLUTION: Plural

PROBLEM: The ambassador was an ally and friend, who owed his post in Washington, D.C. to the Owl's influence and discreet lobbying.

SOLUTION: Singular

PROBLEM: Crimson drapes coat the walls in an alternating pattern of thick velvet fabric and bare, black walls.

SOLUTION:
Plural