It is our obligation to follow the rules and regulations.

The scientist acted as an observer during the experiment.

She obsesses over every little detail.

Her obsession with cleanliness is starting to become a problem.

He has an obsessive personality.

It's odd that he didn't show up to the meeting.

I didn't mean to offend you with my comment.

The police arrested the offender for breaking the law.

He was charged with a serious offense.

I can't think of the answer offhand.