1.定语从句表示原因

表示原因的定语从句，其意义与原因状语相同，可以翻译为“因为”、“由于”等。

Most of these deaths happen in rural areas，where people burn wood and coal to cook food and stay warm．(人教大纲版高二上第68页)

这些死亡大部分发生在农村地区，因为那里的人燃烧木柴和煤炭来烧饭取暖。

此句可以理解为:Most of these deaths happen in rural areas，because people there burn wood and coal to cook food and stay warm．

When Hitler came to power in Germany，Einstein，who was a Jew，found the doors of study closed to him．(人教大纲版高二上第86页)

当希特勒在德国执政时，爱因斯坦发现科学研究的大门对他是关闭的，因为他是个犹太人。

此句可以理解为When Hitler came to power in Germany，Einstein found the doors of study closed to him because he was a Jew．

The danger was very real，especially in the beginning，when little was known about the new disease．(人教大纲版高三第214页)

危险是潜在的，特别是开始的时候，因为那个时候我们对这种疾病知道得很少。