The following passage is given:

Recently an unusually high number of dolphins have been found dead of infectious diseases, and most of these had abnormally high tissue concentrations of certain compounds that, even in low concentrations, reduce dolphins’ resistance to infection. The only source of these compounds in the dolphins’ environment is boat paint. Therefore, since dolphins rid their bodies of the compounds rapidly once exposure ceases, their mortality rate should decline rapidly if such boat paints are banned.

Then there is the question:

Which of the following, if true, most strengthens the argument?

A- The levels of the compounds typically used in boat paints today are lower than they were in boat paints manufactured a decade ago.

B- In high concentrations, the compounds are toxic to many types of marine animals.

C- The compounds break down into harmless substances after a few months of exposure to water or air.

D- High tissue levels of the compounds have recently been found in some marine animals, but there is no record of any of those animals dying in unusually large numbers recently.

E- The compounds do not leach out of the boat paint if the paint is applied exactly in accordance with the manufacturer’s directions.

The "answer" is C, but I don't understand why that is?

Doesn't C have the opposite effect? Since boats don't directly come in contact with sea water after being painted, and the fact that they are exposed to the air for some time before use reduces the chances of these compounds to contaminate the sea. The only choice that seems to me to be relatively correct is B.

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3 Answers 3


The argument is that dolphin mortality should decline rapidly if these boat paints were banned.

If the toxic compounds remained poisonous for a long time then banning the paint would still take some time to have an appreciable effect. However if the compounds become harmless within a few months then a ban would make a difference much sooner. So (C) strengthens the argument.

  • Just to add to TheMathemagician's response, If these compromise dolphins' immune at low levels, the fact that at high levels they are toxic to other marine life (B), adds nothing to the argument being made. I agree B might be consistent with the argument, it does not add to that argument. Commented Mar 18, 2014 at 15:41

"Since boats don't directly come in contact with sea water"...you are adding information which is not given anywhere. All you should know from the text is that boat paint is a source of these compounds. Maybe the paint still leaks these compounds, this is not specified, and being a reading comprehension it does not matter.

Analysing the options: The sentences in A,D,E as well as B are not found anywhere in the given text. Specifically to B, since that would have been your preferred choice, only dolphins are mentioned, no other marine animals.

C: The key sentence is "dolphins rid their bodies of the compounds rapidly once exposure ceases". If the compounds did not break down and become harmless, exposure would never cease.


I eliminate the other answers to get my Answer.

  • A: can't be, because the passage does not tells about change in boat paint
  • B: can't be, because it is too vague, talks about all the marine animals, but passage talks about the harmful effect of compound to dolphins
  • C: may be, because there would be a steep decline in mortality rate of dolphins, ("should decline rapidly if such boat paints are banned"), this means aged boat paint is not that harmful
  • D: can't be ,it contradicts the first line
  • E: can't be, too vague and out of scope, manufacturer's directions has not been talked about

Thus C is the answer

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