Question:
David hit Bill because Mary really liked him.

Who is him referring to in this sentence?
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Answer:
Bill


Question:
Stephen Colbert is funnier than John Stewart since his show has less viewers.

Who is his referring to in this sentence?
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Answer:
John Stewart


Question:
Windows is worse than Linux because it has a lot of viruses.

Who is it referring to in this sentence?
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Answer:
Windows


Question:
John thanked Bill because he was helpful.

Who is he referring to in this sentence?
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Answer:

Bill