(A) ventures way out into an entirely unsupported fanfiction prequel to the stimulus’ Zebra mussel story. It would maybe be the right answer to a question like “what would be the most interesting random additional facts we could add?”

(B) ventures way out into an entirely unsupported hypothetical, even adding on new facts like “the mussels are unsuitable for use with cultured pearls” and “mussels would displace the clams.” You can’t just tack on random additional information in an MSS question – the claims in the right answer must all be supported by the stimulus.

The word “nuisance” is what really kills (C). We do know the mussels clog intake pipes, but not catastrophically. They’re just annoying. In fact, given that the mussels are a nuisance, having to go down there and scrape the mussels from the intake pipes mechanically would fit well with that description.

(D) falls short for a few reasons. The cleanest one is the difference between intake pipes (where water goes into the plants) and discharge streams (where water comes out of the plants). We’re hanging these mussels in the discharge streams, so there’s not much reason to think the discharge water is gonna loop back around to the intake pipe.

Secondly, all we know about removing algae is that it improves water quality, which is pretty broad. There are lots of ways to improve water quality. So we have no reason to believe that the specific way algae removal improves water quality is by removing a thing that would have clogged intake pipes. Like maybe it removes poison – that’d be an improvement too.

(E) is a great data point for distinguishing MSS questions from MBT/Inf questions, because it’s correct despite its support being weak in places.

The stimulus tells us Zebra mussels remove some hazardous wastes and improve water quality. (E) talks about what happens to that waste inside the mussels: it either a) remains in the mussels, or b) gets transformed. Those options are perfectly reasonable – in fact, they’re the only two conceivable options of what could happen to the waste. It can’t just disappear.

(E) does include the assumption that “stuff that contains hazardous waste must be regarded as hazardous waste,” which echoes the part v. whole distinction we commonly discuss. This would not pass the MBT standard, but here, it's the best supported answer.