The correct option is
A Monotreme mammal
Ornithorhyncus anatinus is a semi-aquatic oviparous mammal. Sometimes also called platypus.
(A)Duck belongs to Class Aves.
(B)Dinosaur belongs to Class Reptilia.
(C)Monotreme mammals are egg-laying mammals.
(D)Fossil birds belong to Class Aves.
So, the correct answer is 'Monotreme mammal'.