Which set of fins on a fish body exists as pairs?
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Answer: B. Pectoral and Pelvic.
Explanation
In fish anatomy, the pectoral and pelvic fins are paired appendages corresponding to limbs. These paired fins provide stability, steering, and braking control during swimming locomotion. Pectoral and pelvic fins represent the correct paired fin set found in vertebrate fish. Fishes possess various median and paired fins supported by internal bony or cartilaginous rays. Pectoral fins attach anteriorly near the gill region corresponding structurally to vertebrate arms. Pelvic fins are located more posteriorly on the ventral surface corresponding to vertebrate legs.
Evolutionary transitions from fish to tetrapods involved the modification of these paired fin structures. Aquatic maneuverability depends heavily on the precise hydrodynamic control of pectoral and pelvic fins. Ichthyologists use fin ray counts and positioning to identify and classify different fish species. Dorsal and anal fins are unpaired median structures that prevent rolling during forward swimming. Tail fins are unpaired caudal structures that provide the primary propulsive thrust for movement. Selecting all of these is incorrect because dorsal and anal fins exist as single, unpaired structures.
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