\textbf{200.} In the band structure of a solid, the conduction band is full of electrons and the valence band is also full. What is emitted from it?
\begin{tabbing}
\hspace{4cm}\=(1) resonance electrons -- resonance light \hspace{1cm} \=(2) valence electrons -- resonance light\\
\>(3) resonance electrons -- valence light \>(4) valence electrons -- valence light
\end{tabbing}
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