A, D - Incorrect: The correct idiom is not only… but also; they...had is not parallel to the noun capitalist differentiation. Also, the pronoun they has no clear antecedent. Grammatically it can only refer to the farms, but logically it seems intended to refer to members of the Soviet administration.
E - The correct idiom is not only… but also. Moreover, the placement of toward in toward not only... but toward is not parallel.
B - in addition and also are redundant; as far as production is concerned is wordy.
C - Correct: This answer maintains parallelism within the not only... but also idiom structure.
C is the correct answer.