Answer:
The most closely related are amphibians and reptiles.
The least related are amphibians and mammals
Step-by-step explanation:
Amphibians broke off from reptiles, birds, and mammals around 260 millions years ago and next up are the reptiles which broke off around 225 million years ago. So they are the most closely related
Mammals are the last to break off, around 200 million years ago. So they are the least related to amphibians.