Read the following paragraph and underline the topic sentence.
The most vital difference between Muslims in America and their brothers in Europe is the U.S. enduring emphasis on religious liberty. Religion is given far more respect in the U.S. than in Europe. Think about it. The U.S. is in the midst of a resentful debate over immigration in which many Americans reject “hyphenated （带连字符的） identifies” like Mexican-American as a threat to national unity. Yet while Protestant, Catholic and Jewish Americans may disagree strongly among themselves, the religious basis of their identity is not seriously questioned by anyone. If Muslim Americans are not so readily accepted today, it is not because they are believers. In Europe, by contrast, Muslims are resented and marginalized precisely because their religion threatens strong secular （世俗的） values.
【正确答案】：The most vital difference between Muslims in America and their brothers in Europe is the U.S. enduring emphasis on religious liberty.
【题目解析】：文段开头一句提到美国穆斯林和他们欧洲兄弟之间最重要的区别是美国一直强调宗教自由。之后就围绕宗教展开论述，分别介绍了美国穆斯林和欧洲的宗教，故本段的主旨句就是开头第一句。
