<span>b) Gold existed just beyond the Appalachian Mountains.</span>
<u>The industrialization supposed a strong increase of the population</u>. <em><u>This was concentrated in cities, which were growing with the waves of immigrants from rural areas, attracted by the work in the industries</u></em>.
<u><em>The growth of cities was not accompanied by urban planning, hence the lack of basic services</em></u>: <u>running water, sewerage, etc. The lack of hygiene was absolute.
</u>
<em><u>The correct answer is A</u></em>: <u>Overcrowding</u>.
