because:

　　Because it was wet he took a taxi. 由于下雨他叫了一辆出租车。

　　He was worried because he hadnt had any letter from her.

　　他很担忧因为他没收到过她一封信。

　　as:

　　As David had a passion for walking, we started off on foot.

　　由于大卫喜欢走路，我们就步行出发了。

　　As youre sorry, Ill forgive you. 既然你悔悟了，我就原谅你。

2）还有一些表示原因的状语从句由seeing（that）,considering（that）或now that等引导：

　　Please dont try to back out now that everything has been arranged.

　　现在一切都安排好了，请不要打退堂鼓。

　　Now youre here, you may make yourself useful. 你已经来了，不妨帮帮忙。

　　3）许多用在形容词后的that从句也起原因状语的作用（that 有时可省略）：

　　She was glad that she had controlled herself. 她很高兴控制住了自己。

　　Im disappointed that they cannot come. 他们不能来我很失望。