The bold part given in the sentence below is fixed and correct. Determine the part(s) in the remaining sentence which is/are free from any error and mark the corresponding answer.
About one-third of the dam's electric output goes (A)/ directly in fertilizer production (B)/ for what was previous the (C)/ most fertile area on the planet. (D)
Parts A and D have no error.
B has the preposition 'in' which should be replaced with 'into' to make the sentence correct.
Part C has the adjective 'previous' which should be replaced with the word 'previously' to have the correct structure of the sentence.
Thus option 5 is the correct answer.