a rat-a-tat at the door的用法和样例：
- At the rat a tat of the knocker her heart fly into her mouth.
- There was a furious knock at the door.
- There is a light rap at the door.
- I found a stray cat crying at the door.
- He got parking ticket because he parked his car at the door of a store.
- Some man at the door is asking to see you.