There is a difference between a lack of rain causing the crops to fail, and a lack of rain affecting the growth of wheat. The latter leaves room for the possibility of error by the farmer. While a rain shortage may make things more difficult, an incompetent farmer could still be responsible for the ultimate failure, and its consequences.
That is from looking very closely at the answer choice. Even without seeing the distinction above, the concept of "responsibility" made me question answer choice C. There is no information in the stimulus regarding responsibility, so we are not able to make a valid conclusion about it.