Why isn't option with 'Pomóż mi z napisaniem książki' accepted? :(
"napisać" is a perfective verb, so means not just writing a book but also finishing it. That being said, "Pomóż mi w pisaniu książki" should be accepted, because English you is both singular and plural, so could mean both "ty" and "wy".
w pisaniu książki. which case is it?
pisaniu is Locative (in what?), książki is Genitive (writing of what)
Am I the only one who thinks "help me with writing the book" sounds very strange?
In Polish it is strange too, one can help "napisać", or do not distract "pisać"
Both "napisać" and "pisać" are accepted.