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: Clearly, a notion she hadn't suspected.

SOLUTION: Singular

PROBLEM: Realizing too late, some immortals were able to defend themselves as panic and confusion set in.

SOLUTION: Plural

PROBLEM: Each glide sent her hair rippling, sent his pulse pounding through him with memories of having that body move against him with the same grace.

SOLUTION:
Singular