同学你好，该知识点来自沪江网校《【Uni智能】雅思6.5分一站式VIP-初中起点【全额奖学金班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好。

这句话is often the case with children是定语从句，这句话的主语应该是Joanna was better when the doctor arrived. 所以这是一句非限制性定语从句。按照一般的语序，应该是Joanna was better when the doctor arrived，which is often the case with children. which指代前面整句话。但是因为从句被提前了，所以which需要改变为as。

as is often the case...这是常有的事。

这句话的意思是，小孩子通常就这样,医生一到Joanna就好多了。

希望有帮助到你~