"The expected price drop ....." is a phenomena, so it will have a impact on something else but it wont itself impact. And, possibility is basically a number which diminish or increase. Possibility cannot be impeded or hindered.
(A) This statement is saying the phenomena of "The price drop ...." is itself impacting the agrarian nations, which is wrong.
(B) This statement is saying the phenomena of "The price drop ...." is itself impacting the agrarian nations, which is wrong. And also possibility cannot be impeded, it can get diminished or increased. Hence this option is wrong.
(C) This statement is saying the phenomena of "The price drop ...." is itself impacting the agrarian nations, which is wrong. And also possibility cannot be impeded, it can get diminished or increased. Hence this option is wrong.
(D)
This is correct option. The phenomena of "The expected price drop ....." will have a certian impact on agrarian nations and this will "diminish the possibility .....".
(E) Possibility cannot be impeded, it can get diminished or increased. Hence this option is wrong.