As he is absent, we have to do without him.由于他缺席，我们只好自己做了。

今天的几个句子都是提供理由的：1. The reason is that we badly need it. 2. It's because I don't like it. 3. Because of her carelessness, she failed. 4. I don't know her, and that's why we didn't say hello to each other.