1. (4 points) $6 \square 4 \div 3$, to make the quotient have a 0 in the middle, $\square$ can be filled with $\qquad$ . (list all possible cases)
【Answer】Solution: In $6 \square 4 \div 3$, to make the quotient have a 0 in the middle, then $\square<3$,

so $\square$ can be filled with: $0, 1, 2$.
Therefore, the answer is: $0, 1, 2$.