The most accurate assessments of current extinction rates probably come from studies of..

• A. reptiles, because they are ectothermic and susceptible to population declines during frequent past glacial periods.
• B. birds and mammals, because they are relatively well-known taxa.
• C. marine invertebrates, because of their relatively long and complete fossil history.
• D. insects, because they comprise the vast majority of extant multicellular organisms.