1. It's hard to know how to say this tactfully.
   不知道怎样才能婉转地讲明这件事。
2. You didn't know how eager she was at the time.
   你不了解她当时急切的心情。
3. He knows how to keep his mouth shut.
   他知道怎样保持沈默。
4. He knows how to handle the machine.
   他会操作这台机器。
5. He doesn't know how to do it.
   他不知道该怎么做。

　1个名词解释