The correct option is C Monkey
The blastocyst is a structure which is formed in the early development of the viviparous mammals. Morula undergoes further division and forms a structure called as blastocyst.
In the given options, only monkey is a viviparous mammal. Kangaroo is a marsupial while platypus is semi-aquatic egg-laying mammal. Thus, the correct answer is option C.