in front of the blackboard应该是多了一个空格
in front of表示“在…前面”,指某一范围之外的前面与 before意义相近.其反义词是 behind.
in(at)the front of表示“在…前部”,指的是某一范围里面的前面,其反义词是 at the back of,例：
There is a big tree in front of the house.房前面有一棵大树.
The teacher is standing in the front of the classroom.
老师正站在教室的前部.
咱们总不能让老师站在黑板前部吧!