depends on the ppl, some ppl consider B is ok, some think it's great, if u aren't happy, retake la, if u don't mind spend more money, nothing to argue about here.
next time, 你要分的时候,不要直接跟老师发e-mail说要分,你要先跟他make an appoint to discuss the final mark, including the break downs, 然后去的到时候你也可以按照他们的marking outline自己再算一遍,看他是不是有少给你分得,你在跟他argue. 我基本上只要是essay/short answer format的卷子我都回去要分,总是能要回来。而且要是你那门课有participation mark, 你就跟老师要,participation makr 是最flexible 的。