Mary Beth, Chris, and the sergeant's exam

If Mary Beth had taken the exam, would she have passed it? I think she would have passed the written portion, but I'm not sure she would have done well in the videotape part. She always gets really nervous before court and has to have Chris question her, so I think she may have blown the second part of the exam even if she knew the material asked.

If Mary Beth had passed, though, I think she would have had to wait longer than Petrie to be promoted, since her rank was lower than his. He had to wait two years, so I think she probably would have had to wait three, and the next exam would have been the following year.

Also, what was Christine's rank prior to becoming sergeant? Mary Beth was detective third grade for most of the series, so was that Christine's rank as well? Did Chris score really high to pass to sergeant or did she simply pass but was ranked detective first grade? I don't think her rank is mentioned as far as what grade she was before being promoted.