Yes, the line should be parallel to the triangular faces
What is a triangular prism
A triangular prism is a three dimensional geometric shape that consists of two triangular bases and three rectangular faces connecting corresponding sides of the triangles.
The triangular bases are parallel and identical, and the connecting rectangular faces are perpendicular to the planes of the triangles.
To represent the parallel cross-section of a triangular prism, imagine cutting the prism with a plane that is parallel to one of the triangular bases.