In the sentence, certain words are in bold and numbered from A to E, which are the possible pairs to be interchanged.Choose the pair(s) of words which need to be interchanged to make the sentence grammatically correct and meaningful.

The (A) secret to their (B) flooded bounty was the River Lugg flowing through the middle, (C) silt the valley floor with lime and (D) fertilizing each winter it (E) wonderful.