A solid object with a triangular groove is shown on the left. Which option(s) along with this object can form the combination shown on the right?
Show Hint
For 3D combination problems:
\begin{itemize}
\item Match cross-sections, not outer silhouettes,
\item Check that combined faces form a regular solid,
\item Multiple solutions may exist if internal geometry matches.
\end{itemize}
Step 1: The triangular groove in the given solid indicates that the missing piece must have a triangular protrusion that exactly complements the groove.
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Step 2: When the correct piece is inserted, the combined shape becomes a perfect cuboid (as shown on the right), meaning:
\begin{itemize}
\item All outer faces must become planar,
\item No gaps or overlaps are allowed,
\item The triangular faces must align perfectly.
\end{itemize}
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Step 3: Examine each option:
\begin{itemize}
\item A: Contains a triangular volume that exactly fills the groove — valid.
\item B: Can be oriented to match the triangular cut-out — valid.
\item C: Its curved-looking outline still forms the correct triangular cross-section internally — valid.
\item Option D: Does not match the triangular groove geometry — invalid.
\end{itemize}
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Final Answer:
\[
\boxed{\text{A, B, C}}
\]
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