Answer:

b. Amoeba

Explanation:

Amoeba is the only organism out of the four that reproduces by asexual method. Human being, cow and rat reproduce by sexual method.

Answer will be (b) Amoeba reproduces through asexual method.

More specifically through Binary fission. Binary fission is a type of asexual reproduction, In binary fission one cell divides and forns two daughter cells.

(A), (c) and (d) are incorrect because :-

Human beings, cow and rats are mammals and reproduces through sexual reproduction.

In sexual reproduction there's a fusion of male and female gametes which forms a zygote and eventually gives rise to a genetically different organism.