Translation:Because he is clean, he is nice.
It would be nice to have an exercise that explains the different situations in which to use either...
Yes they are synonyms. Good to know there are several words to mean the same thing (if you intend to not repeat yourself?), isn't it?
The problem is that it isn't indicated that they are synonyms. (if and when they are)
Puisque and depuis were introduced in the same manner as if they were likely synonyms. But a poster on another tread indicates that they are not synonyms but involve different uses of since specifically relating to time or causation. (My words not his).
Du fait que is yet another unexplained instance of since presented as if it was simply another construction similar in every respect to previous examples of since . It may well be such but we have no way of knowing whether that is true.
A student of Duo seeing them all presented as if they were interchangeable could get a correct answer and proceed as if he understood their correct usage when he actually didn't.
"puisque" is definitely causal and no temporal, same family of causal conjunctions as "du fait que" or "parce que"
"depuis que" is definitely temporal and not causal, same family of temporal conjunctions as "quand", "après que", "avant que", "dès que" (+ others, like "à partir du moment où", "du moment où"...)
why is he is nice because he is clean marked as incorrect translation? does it make any difference?
Why do you need to change the word order? Just write it how it is, eh? The sentence doesn't make good sense in any language, c'man.
The possible translations are apparently written by hand. You can't expect them to do every possible variation (though Yoda style would be fun!); but it's easy to expect us to translate as literally as possible.