Photovoltaic cells and hydrogen fuel cells share which of the following advantages? I. No emission of air pollutants
II. Abundance of resource
III. Inexpensive compared to other resources

A. II only

B. I only

C. I, II, and III

D. I and II only

A. describe the model of urban structure most often observed in mega-cities in developing countries. explain how this model differs from common urban structures in north america. b. describe at least two factors leading to the growth of mega-cities in developing or least-developed countries. c. identify and explain two factors that led to the formation of squatter settlements in mega-cities in developing countries.