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.
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Question: Ahead of the ship, the relatively calm seas were washing against slate grey rocks that rose seven or eight feet up out of the waters.

Answer: Plural


Question: " Those aliens attacked us, and earth was destroyed because of what they did.

Answer: Plural


Question: What have the twins done to be put in these coffins ?

Answer:
Plural