The correct option is B Than those a year ago and are going down, even though floods in the Midwest and drought in the South are hurting crops and therefore raising
The sentence presents a contrast- "X, even though Y". Here, X states facts about the prices at producer level and Y that floods and droughts are hurting the crops. In the given sentence, the use of 'raised' is a shift in tense that does not fit the context of the sentence. Also, 'than a year ago' is a bit confusing as to its reference. These errors are rectified by B. In the option A, the same errors are repeated, D and E use the unsuitable 'as' and option C is a fragment where the use of 'and' creates confusion as to what are hurting crops and raising. Thus, Option B is the correct choice.