According to the Oxford Dictionary, a 'sea' must be an expanse of salt water, and it could be used to refer to a large lake. The Caspian Sea fits in both of these categories, so it is arguably a 'sea'.
didn't do great, but a bit sad that I typed all the south American capitals but spelt then slightly wrong (one letter out) and didn't get credit- oh well never mind
I usually get half of my answer from here......
Puzzled