"He always speaks in an interesting way."
Translation:On zawsze mówi ciekawie.
I was marked wrong for 'Zawsze on mówi ciekawie' - a correct answer is listed as 'zawsze mówi ciekawie' - do you leave the subject out in this case?
It is about the word order. If you want to put "on", do it in the beginning of the sentence. "Zawsze on" sounds unnatural.
Why doesn't "ciekawy sposób" change to another cause because it is "w ciekawy sposób"?
I think the answer it's that it's a fixed construction.
Also, technically it's not that something is literally "in" (inside) 'an interesting way'.