Which list of organisms consists of only consumers?
a)mango tree, deer, giraffe
b)grass, parrot, lion
c)mulberry shrub, grass, cow
d)eagle, salamander, hen

D) eagle, salamander, hen

Food chain is a sequence of transfer of food and energy in an ecosystem. An energy is transferred in a successive trophic levels of the food chain. At the base level of the food chain there are plants and other autotrophic organisms which are collectively called as primary producers. These organisms are consumed by herbivores as well as omnivorous animals, they are collectively called as primary consumers. These primary consumers are consumed by small carnivores called as secondary consumers. These secondary consumers are consumed by higher carnivores such as tiger and lion and these are called as tertiary consumers.

Eagle, salamander and hen are collectively called as secondary consumers as these animals are dependent upon other animals for their food requirements.  

coal is not sustainable because it will one day run out.

the unequal cytoplasmic division that  results  in  one egg  and three polar bodies ensures that a fertilized  egg has  ample nutrients  forits journey  to  the uterus.