"A reindeer is eating an apple."
Translation:En ren äter ett äpple.
Oddly, the English plural of reindeer is reindeer too. In Swedish, it's ren in the singular, but renar in the plural. In this case though, since it clearly says A reindeer is eating … you can be totally sure it's just about one reindeer, and therefore it must be En ren äter … in Swedish.
Flera renar äter would be Several reindeer are eating.