(B) says, "Although barite can be harmful to marine organisms, it can be consumed safely by humans."
We're looking for something that can be inferred from taking both passages together, but not from either one individually. Figuring out which points the passages overlap on can helps us to answer this question correctly. Barite, the heavy mineral used in drilling mud, was one of the big overlapping points in both of the passages. Passage B discusses how barite could be environmentally harmful, especially to scallops (line 55). Passage A discusses barite, and details that people who have had X-rays of their digestive tracts have probably consumed barite (lines 16-19). Well, what can we conclude from this? It's safe to assume that barite is probably safe for humans to consume, but it clearly isn't for certain marine organisms (scallops). This is precisely what (B) says. We certainly couldn't conclude this from only looking at Passage A or Passage B, but when we combine their contents, we can infer what (B) is saying. Thus, it's the correct answer choice.
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