FOUND ONLINE: Days of torrential rain in Washington state has caused historic floods that have stranded families on rooftops, washed over bridges and ripped at least two homes from their foundations.
If you cut out "in Washington state", you get "Days of torrential rain has caused..." And that sounds wrong.
So: Days of torrential rain in Washington state HAVE caused historic floods that have stranded families on rooftops, washed over bridges and ripped at least two homes from their foundations.
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