For the seven modern wonders of the world, I took the list that was voted in as the top seven wonders of the world in 2007. Although the polling system for selecting these seven modern wonders of the world was criticised as being un-scientific, I decided to use them anyway. If you want a more Scientific list, you can check out the list of heritage sites that were selected by UNESCO, who have a specific criteria for selection. Alternatively, you can check out the lists of seven wonders of the world according to their different categorisations, e.g. natural wonders, medieval wonders, etc.
Some of the flashcards in this series: