Which Is a Major Reason Scientists Are Alarmed by the Rapid

Which is a major reason scientists are alarmed by the rapid and massive loss of amphibians?

A) It is occurring mainly in regions where human activity is greatest.
B) Many of the declining amphibian species are economically important.
C) Amphibians are biological indicators, so their decline suggests as-yet-unknown environmental dangers.
D) The decline is global and has been very gradual, so it was not noticed until about 2000.
E) Scientists fear the dying amphibians may spread disease to human populations.