狗在抓门，因为它想进来。

The dog is ___scratching at the door because it wants to come inside.

昨晚我们听到有东西在刮窗户。

We heard something ___scratching at the window last night.

指甲刮黑板的声音非常可怕。

The sound of fingernails ___scratching a chalkboard is horrible.