Young american men must register with the selective service system when they reach the age of
18
19
20
21

18

The answer is the first option, 18.

Explanation: The SSS (Selective Service System) is a US agency that keeps information on those potentially subject to military conscription.

The law states that all male US citizens and male immigrant non-citizens are required by law if they are between the ages of 18 and 25, to register in at least 30 days after their 18th birthday.  

answer; obey the closest relative's wishes;

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