B is correct because the word "to" is used to denote the goal. C contains a mistake because the word "for" refers to the person or thing that anything is done for. In this case, the word "of" should be used to denote the items whose prices will rise.
There are no mistakes in the section of the sentence that starts with the letters a), b), and c). Answer option A is valid since the sentence is in the past perfect tense. It is okay to use the word "decided" in this situation.