Answer:
D. Move sentence 13 to the beginning of the paragraph.
Step-by-step explanation:
Moving sentence 13 (Salt used to be so important that it was used as a form of payment in many cultures) to the start of the paragraph will improve its organization. It will give an idea to the readers what the text in the following lines would be.
Option A is incorrect because adding "as a result" before sentence 11 will have bad impact on readability of text. Sentence 11 is not a result of something told before the sentence.
Option B is incorrect because sentence 8 and 9 are already in correct order (logically arranged).
Option C is incorrect because removing sentence 10 will deprive sentence off some important information about salt.