\textbf{180.} In the figure, what are A, B, and C respectively?
\textit{[Figure: A light bulb with parts labeled A (bottom), B (middle), and C (top).]}
\begin{itemize}
\item[(1)] Insulator (glass base), mixture of hydrogen and oxygen
\item[(2)] Insulator (glass base), mixture of argon and nitrogen
\item[(3)] Metal contact points (base), mixture of hydrogen and oxygen
\item[(4)] Metal contact points (base), mixture of argon and nitrogen
\end{itemize}