The correct option is A Amphibia
The pentadactyl limbs exist in animals from dolphin to the horse to the bat and each animals uses the same limb in different way. Every pentadactyl limb has the same base structure of five digits.
Amphibians body has two pairs of limbs. The forelimbs have four toes whereas the hindlimbs have five toes and toes are without claws.
Amphibians limbs are least specialized. These are pentadactyl without claws or nails.
Therefore, the correct answer is option A.