Which of the following represents the correct combination without any exception ?

Option	Characteristics	Class
\((a)\)	Sucking and circular mouth; jaws absent, integument without scales; paired appendages.	Cyclostomata
\((b)\)	Body covered with feathers; skin moist and glandular, fore-lims form wings; lungs with air sacs.	Aves
\((c)\)	Mammary gland; hair on body; pinnae; two pairs of limbs.	Mammalia
\((d)\)	Mouth ventral; gills without operculum; skin with placoid scales; persistent notochord.	Chondrichthyes

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.