What problems have been caused by urbanization in north america?

Can someone me choose a broad topic and area of focus i am really doing this as a tally to see which one most people pick ok water pollution global warming endangered species atmosphere for the !

Read the article titled "trans-saharan migration routes to north africa and the eu: historical roots and current trends." why do tens of thousands of sub-saharan africans try to cross the mediterranean each year? how are these refugees commonly portrayed? (site 1)

The great scientist alfred wegener proposed that continents have moved, while other scientists such as t.c.chamberlin argued against wegener. wegener's ideas eventually won, and are now widely accepted, because: a) wegener's ideas were more beautiful, and so were favored by the intellectual elite.b) wegener's ideas did a better job of predicting the results of new observations and experiments.c) wegener's ideas appealed to dead white european males, whereas chamberlin's didn't.d) wegener's ideas appalled dead white european males, and we all know that in this politically correct era,dead white european males cannot get a fair shake.e) wegener won the nobel prize.