前三门是北京城的正阳门（前门）、宣武门、崇文门合称。自东向西依次是崇文门、前门、宣武门。其中崇文、宣武各取是尚文尚武的意思。这三座城门因为位居于皇城之前，故称为前三门。贯穿于这三个门之间的大街，称为前三门大街。
公司的现代飞思三门小型客车，一年前还未开始销售，也为公司带来了收益。
The company's quirky Veloster three-door small car, not on sale a year ago, contributed to the gains.
第三门户定律——早期开始并连续进行压力测试是防止前两条门户定律破坏您的项目的唯一方式。
Third law of Portal - Stress testing early and continuously is the only way to prevent the first two laws of portal from wrecking your project.
所以，在虚线上签名前，一定要选修不同教授的两门或三门课程，他们的课程编号很高(300,400,3000,4000或是别的什么)。
So, before signing on the dotted line, take two or three courses, from different professors, that start with a high number (300, 400, 3000, 4000, or whatever it is at your school).
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