"En skilpadde drikker vann."
Translation:A turtle is drinking water.
"(en/ei) skilpadde" is the indefinite form, while "skilpadda" (the turtle) is the definite form.
When I answer this with "A turtle..." it corrects me with "One turtle..." How do I know when it is "One" and when it is "A"?
"En skilpadde" can translate to either, which is why we accept both, but I would say "a turtle" is the most natural translation in the context of this sentence.
If you were corrected, there was probably another issue with your translation. Sometimes the system suggests an alternative translation which isn't our default translation, and it can be a little confusing.