Find out the incorrect part of the following sentence.
Lack of sanitation in student dormitories are a major cause of disease in some areas of the country.

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