How to find the correct answer?

Answer B doesn't say a word about any environmental issue related to the oil-well drilling or mud. I truly don't understand why is it the main point of each passage? It simply doesn't make any sense to me. Please educate me on this.

Hi @Alyona1983, We can see by reading both passages that a primary purpose of each passage is to describe the general composition and properties of drilling mud, since both passages go into detail about what’s described in (A). For example, the entire first and second paragraphs of passage A are devoted to this, as are the second and third paragraphs of passage B. It doesn’t have to be the only primary purpose of each passage, but it certainly is one of the primary purposes. Hope this helps! Feel free to ask any other questions that you might have.