Find the meaning of the underlined phrase in the given sentence from the given options.
He was really tired of finishing all the accounts for auditing as he did not hit the sack for more than 36 hours.

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