He's like a walking dictionary.

他简直是个活字典



leave me alone.

别管我，让我静静



I ran into an old friend in the shop yesterday.

我昨天偶遇了一位老朋友



There is nothing I can do.

我什么都不能做



There is nothing wrong with me.

我没事



They're doing it under the table. =secretly

他们在秘密地做此事