$$\left. \begin{array} { l } { A = \{ n | 2024 } \\ { B = \{ n \lt 21 | 0 \lt n \leq 2 \} } \\ { B = \{ n \lt 2 \} } \\ { L = \{ n \lt 2 | 3 \leq n \lt n \} } \\ { A U B = ? } \end{array} \right.$$
$A=n$
$n\in \mathrm{C}$
$A=n$
$n\in \mathrm{R}$
