Choose the best option to complete the following sentence.
After months of investigation, the committee concluded that the financial discrepancies were the result of __________ errors rather than intentional fraud.

He became rich overnight. What part of speech is 'overnight'?

The nightingale is a singing bird. In this singing is a/an --

I Came home after the rain -----.

The Doctor took the round in the hospital. Here 'round' is a/an ---

Alumni is the plural from of