An idea is most likely to represent “common knowledge” if: It can be readily obtained in an encyclopedia. The idea has already appeared in a published work. The idea has been around for more than a decade. It can be safely assumed that the readers and the author are both thoroughly familiar with the idea and its source.

An idea is most likely to represent "common knowledge" if it meets the following criteria:

1. It can be readily obtained in an encyclopedia: Encyclopedias are a source of general knowledge that is widely accepted and recognized. If an idea is included in an encyclopedia, it is likely that it is considered common knowledge.

2. The idea has already appeared in a published work: Published works are often peer-reviewed and widely read. If an idea has been published, it has been exposed to a large audience and is likely to be known by many.

3. The idea has been around for more than a decade: The longevity of an idea can contribute to its status as common knowledge. If an idea has been around for a long time, it has had more opportunity to be disseminated and accepted by the public.

4. It can be safely assumed that the readers and the author are both thoroughly familiar with the idea and its source: If both the author and the readers are familiar with an idea, it is likely that the idea is common knowledge. This familiarity suggests that the idea is widely known and accepted.