Explain why you think Kunal's parents measure him by putting a pencil mark on the door.

Kunal's parents likely measure him by putting a pencil mark on the door as a way to track his growth and development over time. By marking his height on the door, they can visually see how much he has grown and compare it to previous measurements. This can be a fun and interactive way for parents to track their child's physical growth and development, and can also serve as a sentimental keepsake to look back on in the future.

The provided context does not mention anything about Kunal's parents measuring him by putting a pencil mark on the door. Therefore, I cannot answer this question.