Answer:
B) Not knowing how to get the teachers attention properly
Explanation:
It is very normal for small children, and several adults also, to not know how to properly get the attention of other people, specially those very relevant, significant or important individuals. A teacher is very important for a small child, and small children also have a tendency to be easily frustrated (again similarities with adults are only a coincidence).
Since Robert doesn't know how to get his teacher's attention, he gets frustrated and starts hitting her, because he doesn't know what else to do.
