What is urbanization?
a. a process in which an increasing number of people move to cities and suburbs
b. a process in which the rural population of a region grows
c. a process in which the world's number of megacities decrease
d. a process in which a decreasing number of people live in developed regions

Urbanization is the process in which the human population is increasingly more urban, that is, settled in the urban areas -in cities and in the suburbs. So urbanisation is the process of people moving to cities and to suburbs - the correct answer is:
A. a process in which an increasing number of people move to cities and suburbs 

What exactly do you mean