The most serious aspect of amphibian loss，however，goes beyond the amphibians themselves．Scientists are beginning to think about what amphibian （42）___ means for the planet as a whole．If the earth is becoming unlivable for amphibians，is it also becoming unlivable for other kinds of animals and human beings as well？
Scientists now believe that amphibian decline is due to several environmental factors．One of these factors is the （43）___ of habitat，the natural area where an animal lives．Amphibians are very （44）___ to changes in their habitat．If they cannot find the right conditions，they will not lay their eggs．These days，as wild areas are covered with houses，roads，farms，or factories，many kinds of amphibians are no longer laying eggs．
There are a number of other factors in amphibian decline．Pollution is one of them．In many industrial areas，air pollution has （45）___ the rain，which then falls on ponds and kills the frogs that live there．In farming areas，the heavy use of （46）___ on crops has also killed off amphibians．Another factor is that air pollution has led to （47）___ levels of ul