3. $\mathbf{C}$ is the set of complex numbers, let the set $A=\left\{z \mid z^{18}=1, z \in \mathbf{C}\right\}, B=\left\{w \mid w^{48}=1, w \in \mathbf{C}\right\}, D=\{z w \mid z \in A$ ， $w \in B\}$. Find the number of elements in $D$.
3. $z=\mathrm{e}^{\frac{2 k \pi_{i}}{18}}, w=\mathrm{e}^{\frac{2 l k_{i}}{48}}(k, l \in \mathbf{Z})$, then $z w=\mathrm{e}^{\frac{2(8 s+33) x_{i}}{144}}$. Since $(8,3)=1$, $8k+33$ can represent all integers, hence D contains 144 elements.