I am struggling here and read this passage several times I must be missing something. My understanding from reading the paragraph is that these compounds are toxic and that they need to be banned… How does the fact that the compounds might be harmless strengthen this argument? The correct answer is the 3rd one. I had answered 2.
So the conclusion here would be that the Dolphins mortality rate should decline quickly once the boat paints in band.
The basis for that conclusion is that once a dolphin stopped being exposed to the compound, the compound is quickly removed from their bodies.
C is saying that once the boat paints are banned the remnants of the boat paint (with the harmful compounds) which is in the water would quickly break down into harmless substances. So, the dolphins would stop being exposed very quickly, which supports the conclusion that the death rate would decline quickly.
B is saying that the compounds are harmful to other animals however this does nothing to strengthen the conclusion. It does not suggest in any way that banning the boat paints would cause the dolphins’ death rate to RAPIDLY decline .