because +句子；如果this后面还有内容可以构成句子.例如I didn't go out because this was a rainy day
because of + 名词;如果this是代替某个词语,例如I don't have a raincoat. I didn't go out because this.这里的this,指的就是我没雨衣,这个事实,是作为一个代词出现在句子中的.