Difference "retain", "keep", "maintain"?

English as a Second Language English Vocabulary, Grammar and Idioms
1

What is the difference between the three mentioned verbs?

All of them represent almost the same meaning (from my point of view).

Peter

2

Hi,
“Keep” and “retain” are almost the same.However, “retain” is formal.
But “maintain” means look after/keep smth in good condition:
Who is responsible for maintaining the roads?
Regards,
Morteza