C21 Is It a Habit to Use It

"Knock, knock, knock!"

Zhai Yaotian knocked on Cheng Yu's door.

This was the third time he had come to knock on the door. If Cheng Yu continued to choose not to see or hear, he would continue to knock on the door for the fourth and fifth time, or even more.

Cheng Yu was also annoyed by the tireless sound. He zipped up his suitcase, checked all the tickets and passport documents