他对于缺席会议的解释是什么？

What was his ___explanation for missing the meeting?

你能给我快速解释一下这台机器是如何工作的吗？

Could you give me a quick ___explanation of how this machine works?

对于这种奇怪的声音，一定有一个合乎逻辑的解释。

There must be a logical ___explanation for this strange noise.