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: His concentration since Iseo left Compostela fell completely to his training.

SOLUTION: Singular

PROBLEM: The spaghetti straps and the slit in the leg made the dress all the more impressive.

SOLUTION: Plural

PROBLEM: The biggest challenge for indie authors is finding an audience.

SOLUTION:
Singular