Given food web contains some missing organisms $A, B, C$ and $D$. Identify these organisms and select the correct answer
$A-$Deer, $B-$Frog, $C-$Foxes, $D-$Sparrow
$A-$Dog, $B-$Squirrel, $C-$Deer, $D-$Hawks
$A-$Cat, $B-$Eagle, $C-$Cow, $D-$Rat
$A-$Eagle, $B-$Sparrow, $C-$Dog, $D-$Cat
In pond ecosystem, diatoms represent
When food energy passes from herbivores to carnivores
Water plants provide ....... to water animals
Secondary productivity is