Orangensaft and Appfelsaft are compound nouns. http://goo.gl/IyTdGF
- der Appfelsaft = der Apfel + der Saft = Noun + Noun (no linking element) http://goo.gl/KPOcYs
- der Orangensaft = die Orange + der Saft = Noun + en + Noun http://goo.gl/pn9y5o
So as you can see it is not plural Orangen, but actually singular Orange that first loses its ending -e and then the linking element en is used to combine two nouns.
Because der is masculine nominative.
But the apple juice is the direct object in this sentence, the thing directly affected by the action "drink", so it has to be in the accusative (not nominative) case.
Thus you would need the masculine accusative article den.
However, the English sentence just uses "apple juice" -- i.e. identifying the substance in general -- rather than "the apple juice" (referring to a particular quantity of apple juice that you had been speaking about before).
So even den Apfelsaft would be wrong in this sentence because it's not a correct translation for "apple juice":
Yes. sie is used for both "she / her" and for "they / them".
You can tell the difference between "she / they" by the verb ending: -t for "she" and -en for "they" -- sie trinkt "she is drinking" versus sie trinken "they are drinking", for example.
You usually cannot tell the difference between "her / them" -- *ich sehe sie" can be either "I see her" or "I see them".
it would've been better to make us translate sentences from English to German ..like more !!
Rumour says that it's a business choice: translating into German is harder and frustrates/scares away more "casual" users, so you get fewer ad impressions than if you keep the course easier.
What some people do is, once they've become reasonably comfortable with the language, do "the reverse course", i.e. the course "English for speakers of German", in which case most of the translations will be into "your" language (meaning German here, since you're pretending to be a German speaker).