In his current age, Yifan loves to ask questions all the time. The typical types of the questions are: “What” and “Why”.
What is this?
What is on this?
Why this stone is red?
Why this brick is missing?
Why there is no gas hole on train?
Why are you standing here?
Why look at me?
Obviously, he is trying very hard to form an inner mapping of the external world in his brain. He is exploring curiously, and learning happily.