GRE中阅读的代词怎么判断是什么！

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The Fourteenth Amendment to the United States
Constitution, ratified in 1868, prohibits state governments
from denying citizens the "equal protection of the laws."
Although precisely what the framers of the amendment
meant by this equal protection clause remains unclear, all
interpreters agree that the framers' immediate objective was
to provide a constitutional warrant for the Civil Rights Act
of 1866, which guaranteed the citizenship of all persons
born in the United States and subject to United  States
jurisdiction. This declaration, which was echoed in the text
of the Fourteenth Amendment, was designed pri marily to
counter the Supreme Court's ruling in Dred Scott v. Sandford
that Black people in the United States could be denied
citizenship.  The act was vetoed by President Andrew Johnson,
who argued that the Thirteenth Amendment, which abolished
slavery, did not provide Congress with the authority to extend
citizenship and equal protection to the freed slaves.
Although Congress promptly overrode Johnson's veto,
supporters of the act sought to ensure its constitutional
foundations with the passage of the Four teenth Amendment.

这两个红色的act虽然长得一样，但是指代的内容却大相径庭啊。一开始读没读懂。多了几遍都觉得后面逻辑很混乱。最后看别人的翻译才知道这两个act指代的内容不一样。
第一个act指代：Thirteenth Amendment中的Dred Scott v. Sandford
第二个act指代：Civil Rights Act

同志们有没有好的方法或者推荐书或者博客，来找准代词的指代对象呢！