The advent of chemical fertilizers led the farmers in a certain

The advent of chemical fertilizers led the fanners in a certain region to abandon the practice of periodically growing a ""green-manure"" crop, such as alfalfa, in a field to rejuvenate its soil. As a result, the soil structure in a typical farm field in the region is poor. So to significantly improve the soil structure, fanners will need to abandon the use of chemical fertilizers.

The argument relies on the assumption that

(A) most, if not all, farmers in the region who abandon the use of chemical fertilizers will periodically grow alfalfa

(B) applying chemical fertilizers to green-manure crops, such as alfalfa, has no positive effect on their growth

(C) the most important factor influencing the soil quality of farm field is soil structure

(D) chemical fertilizers themselves have a destructive effect on the soil structure of farm fields

(E) many, if not all, fanners in the region will not grow green-manure crops unless they abandon the use of chemical fertilizers

negating the main point:
farmers need not have to leave CF to improve soil structure
given that a) alfafa can improve soil structure b)CF has degraded the soil strcture

pre-think:
1. what if withouting abandon they still can improve soil structure by doing something x

look at the options:
(A) most, if not all, farmers in the region who abandon the use of chemical fertilizers will periodically grow alfalfa
even if most farmers who abandon CF will not grow alfafa, then soil will further degrade, it is weakinig.

(B) applying chemical fertilizers to green-manure crops, such as alfalfa, has no positive effect on their growth
even if CF has positive effect on growth of crops, it is not relevant at all!.

(C) the most important factor influencing the soil quality of farm field is soil structure
not relevant at all

(D) chemical fertilizers themselves have a destructive effect on the soil structure of farm fields
its what given in the passage.hence cannot be assimption

(E) many, if not all, fanners in the region will not grow green-manure crops unless they abandon the use of chemical fertilizers
if farmers growth both alfafa and use CF, then there is a chance soil structure will improve. hence its a correct answer