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.
One example: They both let out relieved breaths at the doctor's words.
Solution is here: Plural
Explanation: "relieved breaths" is the object of the sentence which is plural.

Now, solve this: A few days ago he had been investigating a minor theft.
Solution:
Singular