Notice that the question tests subject-verb agreement: "each" is singular, so the verb should be "struggles," which limits the choices to (D) and (E). The first difference between these two choices is "required to produce" and "producing." Since the sentence concerns producers of saffron who produce it from flowers, "required to produce" better reflects the meaning. The other difference is"of" and "from" at the end of the underlined portion. Blooming "of" flowers is idiomatic, so this is another reason to choose (D) instead of (E).