How to tell if a package came from stable/testing/unstable?

Is there a way to display which packages (say, on a Knoppix 3.8 HD installation) came from testing, which from stable, and which from unstable?

One would assume the package management system would know to upgrade a given package from the distribution it originally came from, wouldn't one? ("Distribution" here meaning "stable/testing/unstable".)

Look in /var/lib/apt/lists, this should help.

Code:

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ls /var/lib/apt/lists

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