In this task you are given a sentence. You must judge whether the object of the main clause is singular(like: apple) or plural(like: apartments). Label the instances as "Singular" or "Plural" based on your judgment.

Suddenly he heard the echo of footfalls against his marble floors.
Singular

Under his fingertips, he felt her pulse quicken as something loud crashed off in the direction of the stairwell, echoing down the corridors.
Singular

Where did the staff keep all the supplies ?

Plural