In other words, when they become citizens of the United States, they can no longer be a citizen of another country.
換句話說,當他們成為美國公民時,他們就不再是其他國家的公民了。
They have to give up their citizenship in the other country.
他們必須放棄其他國家的公民身份。
This can be difficult for people who love their home country very much,
對于熱愛自己祖國的人來說,這將是一個非常艱難的決定。
because they might feel that they are betraying (or doing something against) the country they grew up in.
因為這會讓他們覺得他們在背叛(或做不利于它的事)自己從小長大的祖國。
People who become U.S. citizens also must promise to obey (or follow) the laws of the United States and to defend (or help protect) the country's Constitution (or its most important legal document) and laws.
成為美國公民的人還必須承諾遵守美國法律并捍衛(或保護)美國憲法(或其最重要的法律文件)和法律。
This might mean speaking up (or saying something) when one sees that Americans' rights are in danger of being taken away.
這就意味著當一個人看到美國人的權利有被剝奪的危險時就要勇于站出來發聲(或發言)。
Finally, people who become U.S. citizens must promise to serve (or do important work for) the country if it is needed.
最后,如果祖國有需要,成為美國公民的人必須承諾為它服務(為它做重要的工作)。
They also have to promise to serve in the U.S. military if needed.
如有需要,他們還必須承諾在美國服兵役。
Young men who become U.S. citizens need to register (or sign up) with the Selective Service so that their name is on the list of people who can be called to serve in the Army if there is a war.
成為美國公民的年輕人需要到美國兵役登記局登記(或報名),這樣的話如果發生戰爭,就能召集名單上的人入伍。
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