Which of the following respires by gills?

Among vertebrates,...$A$... use gills whereas reptiles,birds and mammals respire through the ...$B$... Amphibians like frogs can respire through ...$C$... also. Mammals have a well adapted respiratory system. Select appropriate choice for the blanks $A, B$ and $C$ to complete the given $NCERT$ statement.

$A$ : The lungs of birds are provided with air sacs.
$R$ : Air sacs supplement respiration.

Which of the following is $NOT$ a respiratory organ in the phylum $Arthropoda$?

Specialised respiratory organs are absent in:

Which function is served by the tracheal system in insects?