The teacher checks the student's IQ.

The teacher asked: "Who is the child of your parents, but not your biological brother?" Ti replied: "That's me, Ti". The teacher is very satisfied.

Teo's turn, the teacher also asked: "Who is the child of your parents but not your biological brother?". Teo scratched his head and scratched his ears: "Let me go home and think."

When he got home, he couldn't think of anything, so he went to ask him: "Who is your parent's child but not your biological sibling?". Tieu immediately replied: "That's Tio, who else is there?"

The next day, Teo excitedly went to class to show off to the teacher that it was like a nail: "I know who it is, it's my friend Teo".

The teacher muttered: "Why is that, it must be Ti?".