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: The race is on.

SOLUTION: Singular

PROBLEM: Clearly, a notion she hadn't suspected.

SOLUTION: Singular

PROBLEM: The new arrivals stood quietly inside the door as if they were about to engage in a duet.

SOLUTION:
Plural