Working in = the field of I am working in dentistry. Work at = a place I work at a factory. Working on = a goal I am working on my BA

*The difference between "work in"and "work at" is: -"work in" means "find a place/position for..." Example: Kim has just graduated the Banking Institute,so she is trying to work in a bank now.(she is trying to find a place in a bank) -"work at" means "have a position and in action" Example: Kim is a very successful CEO,she works at the BIDV bank now. *"Now" is an adverb of time ant its position is in the first or final of a clause/sentence.