GRE课程
The crustaceans known as harpacticoids are very widespread in marine sediments, where they feed on microorganisms by ingesting the sediment particles to which the microorganisms adhere. Heavy metals, such as those found in industrial pollution, readily adhere to sediment particles. Harpacticoids are poisoned by heavy metals but are unaffected by most other pollutants. Therefore the concentration of harpacticoids in an area is a good indication of whether that marine environment contains heavy metals.
Which of the following is an assumption on which the argument relies?
Industrial pollution is the principal source of heavy metals in marine sediments.
Harpacticoids are the only crustaceans that feed on microorganisms by ingesting sediment particles.
Harpacticoids are more susceptible to poisoning by heavy metals than are other marine organisms.
The microorganisms that harpacticoids feed on are not killed by pollutants that are harmless to harpacticoids.
The microorganisms that harpacticoids feed on absorb heavy metals.
Select one answer choice.
