"The dogs are mammals."
Translation:Οι σκύλοι είναι θηλαστικά.
Oh, no. ο σκύλος (singular)/οι σκύλοι (plural) is correct, but there is no such thing like το σκύλο and τα σκύλα. There is το σκυλί/τα σκυλιά (basically the same as ο σκύλος/οι σκύλοι, but some people use this one to include female dogs as well, since ο σκύλος is masculine.). There is also η σκύλα/οι σκύλες, just for female dogs. ^.^
The link does work for me. But, just to make your life a bit easier (and also because sometimes, the links are a bit buggy on the app), the word θηλαστικά is neuter plural, and it refers to the word animal that's also neuter. It's implied, but that's how this one works. ^.^