The figure has 5 faces. A plane can be chosen that slices all of them, hence results in a 5-sided cross-section figure.
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<em>How</em>
Draw a line on one of the triangular bases that is not parallel to any edge. It must intersect 2 of the 3 edges. Draw a line on the opposite triangular base parallel to the first line, but that intersects the edge parallel to the one not intersected by the first line.
The plane containing the two lines you drew will intersect all 5 faces of the prism.
