"The boy does not know that there is a pink hippo."
Translation:Το αγόρι δεν ξέρει ότι υπάρχει ροζ ιπποπόταμος.
Your answer is correct ( I am greek) , that's what I put . They just have messed up the translations a little bit ... :)
It just happens that this case is a generic one. The boy does not know that there is such an animal (a pink hippo) in general, so "Το αγόρι δεν ξέρει ότι υπάρχει ροζ ιπποπόταμος", without an indefinite article, makes sense as a translation in Greek! ^.^
Indeed it does :) I just think it should be an alternative acceptable answer... because it is something that comes up on a unique occasion .It's alright though ^.^
I would say that "The boy does not know that there is a pink hippo" is actually a specific not a generic sentence in English. It sounds like the boy doesn't know there is a pink hippo "in the zoo"/"in the garden"/"in the bathroom". To be generic you'd need to include the "such a thing as...."
However, as this a Greek course, not an English one, I take it the key point here is that if it is specific then "ένας" should be included, but if it is generic, then it should be left out? I have often found the inclusion or not of the definite article a bit confusing.
In the earlier example in this lesson, when i translated ´The crocodile is a dangerous animal´, I was marked wrong for omitting ´ένα'. Is this not another such case? The English sentence is surely generic not specific.
In the example you stated, both versions should have been accepted. In this case, however, it would sound unnatural if "ένα" is not omitted.
That is, if we say that the sentence here is a general statement ("...that there are pink hippos"). If it's not a general statement, but we're talking about some specific pink hippo, yes, it's better to include "ένα".
G.Georgopoulos - Apologies - my query was unclear. I meant ´ín the case of the crocodile´ the English sentence is generic. You say both versions should have been accepted, but the one omitting the article was not. I presume that will be corrected - thank you.