The correct option is D 50 lakhs
A town is a small urban centre, with a population of less than 1 lakh.
A city is an urban centre, with a population between 1 lakh and 10 lakhs.
A metropolis is a large city, with a population of more than 10 lakh inhabitants.
A megacity, which combine several cities, have a population of more than 50 lakhs.