解释以下句子中为什么要填括号中的词,以下都是选择题,括号中的为正确选项。
1.----What did the report say?
----He said that the UFO (was traveling) from the east to the west when he saw it.
2.----Why did the teacher (get) angry with Tony.
----Because he did some(painting) on the wall of the classroom.
3.----Is it the library from (which) you borrow books?
----Yes,I often borrow books from it.