Regarding Class - Chondrichthyes : Assertion (A): In Chondrichthyes, air bladder is absent. Reason (R): They have to swim constantly to avoid sinking. Regarding (A) and (R) :

Question

( a ) Both A and R are correct but R is not the correct explanation for A
( b ) Both A and R are correct & R is the correct explanation for A
( c ) A is incorrect but R is correct
( d ) A is correct but R is incorrect