—— in his study, he didn't notice that the teacher had come up to him A Buried B. Burying himself

应该选buried，

bury 有“使专心于，使沉浸于”的意思

句子的意思是：他埋头于学习，以至于老师走到他跟前都没有注意到。

通俗点可以这么理解：his study bury him （学习使他沉浸于其中），所以he是被bury的，也就是be buried in his study，要用被动态