Thanks for the question! So this argument starts off with its conclusion: that rapid population growth can be disastrous for a small city. Why? When too many people move in at the same time, city services get overloaded, and city budgets don’t allow for the immediate hiring of new staff.
Now we’re asked for something that would strengthen this argument. (C) tells us that some large cities can absorb rapid population growth more readily than small cities. But honestly, this is quite irrelevant; it doesn’t matter what large cities can or can’t do, we’re concerned here about how small cities react, which we’re already told in the stimulus. We don’t need to benchmark it against large cities.
Hope this helps! Feel free to ask any other questions that you might have.