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Complete the landlord's observation about two very unhelpful roommates.
While Greg _________________________ video games, his roommate _________________________ on the sofa, and the kitchen sink overflowed!
The correct answers are was playing and was sleeping.
We use the past continuous to describe two or more actions happening at the exact same time in the past, often joined by the word "while." Both subjects ("Greg" and "his roommate") are singular, so they both take "was."