This type of question is definitely one of the more vague ones. We need to have an overall understanding of the passage, and a reasonable interpretation of the meaning. However, answer A is definitely the best answer here.
Remember that we're not dealing with a CR problem - the primary purpose of a passage is not the same as the conclusion of an argument. The point about economists using these indicators is simply a bit of background to the main topic of the passage, which is the strengths and weaknesses of these different types of indicators. Look up the word 'utility' in a good dictionary (such as lexico.com) and I think you'll agree.