\[\boxed{\mathbf{80.}}\]
\[\textbf{а)}\ A \cap B \cap C\]
\[\textbf{б)}\ A \cap \overline{B} \cap C\]
\[\textbf{в)}\ \overline{A} \cap B \cap \overline{C}\]
\[\textbf{г)}\ A \cap \overline{B \cap C}\]
\[\textbf{д)}\ \overline{A \cap B \cap C}\]