I think stained because they are now stained
<span>There is a crashing sound from the piano, which Herbert is playing.</span>
This is persuasive writing written with the persuasive technique technique of Logos, which is the use of persuasion to someone's logical reasoning and using supportive facts to back it up. All the the facts presented here about the testing they do and filtering process used appeals to one's logical reasoning. That said, reading through the answers, the author's motivation is to sell the water, so the facts must speak to its credibility. Therefore, we know this is not a consumer, we know there is a motive to sell, so D is the best answer.
