Fill in the blanks with the most appropriate words.
A preposition is a word which comes before a noun or a pronoun and establishes a relationship between the elements of a clause or words. Option A)how long / from/ to is correct as 6000 km indicates distance and therefore, long must be used, from and to indicate a source and a destination respectively. The other options are wrong as much, fast and wide are not appropriate to use here. These uses don't fit in the given question. The correct answer is A) how long/ from/ to.