Translation:Because the class is difficult, I study at home.
Let me start by saying I love this course (and all the courses on Duolingo in general), but small note to the developers: when the sentences start getting this long, it is actually harder to read them written in all kana- ...maybe introduce a few more kanji toward the beginning/middle of the course...
see also https://www.duolingo.com/comment/23065428$comment_id=23682266 (go -> ngo) and https://www.duolingo.com/comment/23262674 (ga -> nga)
I think it's just like this because of what it is being asked to translate to.
”Because the class is difficult, I (will) study at home." じゅぎょうがむずかしいから、いえでべんきょうします。
”I (will) study at home because the class is difficult." いえでべんきょうします。じゅぎょうがむずかしいから。
When I took the class the teacher used separate sentences when using から as because, probably because as V2Blast mentioned, verbs come at the end of a sentence. A comma probably would work too, though I'm not sure.
I put "The classes are hard, so I study at home". Weird... I'm not a master at Japanese by no means. However, I'm pretty sure both are correct and you can determine which one is the most accurate by context. Not to mention, I personally find my translation more natural. "kara" can mean "because" or "so". In addition, it depends on what situation this statement is being said in on whether "classes" or "class" is the correct term
I understand though why this course has so many quirks to it. Japanese can be very context heavy and so unlike English and other languages. Statements can have multiple translations depending on the context and the person reading or listening to them simply have to discern for themselves which translation is the best.
I do find this course useful though for practice and maybe some basic study if you can't get a hold of resources yet. However, to anyone in that situation, I want to urge them not to take some of the course's "right or wrong" judgments too seriously. Japanese is a very versatile language, but that also gives beauty to the language and makes it how you can say many things with just one grammar rule.
The "do" makes it unnatural-sounding in my opinion, gives it a sort of faux-Shakespearean vibe. Just "I study at home" is far more common and just as grammatically correct. Even if it may be grammatically correct (I'm not a native English speaker so I'm not 100% certain), it's always best to use simple, straightforward translations on Duolingo.
The commas in Japanese are not reliable since there are no strict rules for the usage, only guidelines. It's often in the place where you would make a pause while speaking. Depending on the author of a text, there might be a comma or not in an otherwise identical sentence.
Sadly it's like with most other ambiguous words or grammar; It depends on the context whether から means "because" or "starting from".
It's similar to the English "since" in that regard...
Without context, it could mean both. That's why google translate often translates Japanese so badly compared to other languages.