三权分立是指国家的立法、行政、司法分别由三个机关独立行使，并互相制衡。美国是一个联邦制国家，采取的是三权分立制度。如下图所示：
1、立法分支（Legislative branch)负责制定法律，归于美国国会（Congress)，美国国会由参议院（Senate)和众议院（House of Representatives)构成。
2、行政分支（Executive branch)负责执行法律，归于美国总统（President)，任期四年，并可连任一次。
3、司法分支（Judicial branch）负责解释法律，归于联邦最高法院（Supreme Court)，最高法院共设包括首席大法官（Chief Justice）在内9名大法官。
接下来我们看一下真题中所暗含的文化背景吧。
①On a five to three vote, the Supreme Court knocked out much of Arizona’s immigration law Monday—a modest policy victory for the Obama Administration. But on the more important matter of the Constitution, the decision was an 8-0 defeat for the Administration’s effort to upset the balance of power between the federal government and the states.
⑦Some powers do belong exclusively to the federal government, and control of citizenship and the borders is among them. But if Congress wanted to prevent states from using their own resources to check immigration status, it could. It never did so. The administration was in essence asserting that because it didn’t want to carry out Congress’s immigration wishes, no state should be allowed to do so either. Every Justice rightly rejected this remarkable claim. (1-2013-T4)
40. What can be learned from the last paragraph?
[A] Immigration issues are usually decided by Congress.
[B] Justices intended to check the power of the Administration.
[C] Justices wanted to strengthen its coordination with Congress.
[D] The Administration is dominant over immigration issues.
这是13年英一的第4篇阅读，主要考查美国三权分立，the Supreme Court（最高法院）knocked out推翻亚利桑那州移民法的多项条款，这其实对联邦政府而言是一场小的胜利（modest victory），但是大法官以8:0判决联邦法案失败，不会让联邦政府权力高高在上。阅读题第40题问可得出的结论是什么，抛开阅读文章，在了解美国文化背景的情况下做这道题的思路如下：B项中“dominant”意为“在······占主导地位”，这明显违背三权分立原则，直接排除；C项Justices（司法）加强（strengthen）与立法分支（Congress）之间的合作（coordination），违背三权之间相互制衡；D项中“check”意为制衡，明显为正确答案。可见，美国文化背景知识的重要性，它对我们的影响是潜移默化的。
