1、to beat chalk dust from erasers
彈掉黑板擦上的粉筆灰

2、The teacher beat chalk dust from erasers.
老師撣掉黑板擦上的粉筆灰。

3、Yes, the classroom is always a comfortable working condition except some chalk dust still.
是的，課室雖然還有粉筆塵，但仍然是很舒適的工作環(huán)境。