The correct answers are:
Air pollution, housing shortages, overcrowding, water pollution, and water shortages.
Urbanization is the process in which many people that used to live in rural areas migrate to live to urban centers. This process started a few centuries before during the Industrial Revolution to the point that today urban populations are bigger than the rural ones around the world. But it has some negative effects. Pollution, in general, is bigger in cities due to urban traffic, vehicle congestion, poor waste collection, and industrial waste. Cities many times exceed the natural capability of absorbing the waste they produce that pollutes the air and the water, which results in a large amount of smog in the air and contaminated waters. Also, cities are large water consumers, which added to the fact that many water sources are contaminated, it generates water shortages. Moreover, since more and more people tend to agglomerate in the same urban area, if the city doesn't present the resources to satisfy their needs it results in housing shortages and the concentration of poor people in slums. Another side effect of the agglomeration around an urban center is the overcrowding, which can be seen in both central and peripheral regions.