The correct option is D contributing
Option D: 'Contributing' means 'to help to cause or bring about'.
This word is most suitable, as it completes the sentence in meaning.
If something contributes to an event or situation, it is one of the
causes of it. Here 'factors' has been used in the sense of cause 'low productivity in agriculture'. If you
contribute money or resources to something, you help
to achieve a particular purpose.
Hence option D is correct.
Option A: 'Producing' means 'to create or form'.
Option B: 'Showing' means 'to exhibit, in order to make something visible'.
Option C: 'Resulting' means a consequence of something.
These words do not provide the required meaning to the sentence, hence A, B and C are incorrect.