sit back = 1. to sit comfortably: Sit back in your chairs.
2. to make no effort: He sat back while others did the work.
sit down = to rest yourself in a chair, on the floor, etc: We sat down on the nearest seat.
sit in = 1. to be present or participate as a visitor at a discussion or music session.
2. to act as a substitute: She sat in for the vacationing news anchor.
3. to take part in a sit-in.…
