Code talkers transmitted messages over military telephone or radio communications nets using formally or informally developed codes built upon their native languages. The code talkers improved the speed of encryption and decryption of communications in front line operations during World War II
<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.
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<em><u>The correct answer is A</u></em>: <u>Overcrowding</u>.
