Two parallel lines are lines that do not meet even with continuous extension of their length. While two lines are perpendicular when they form a right angle to each other at the point where they meet.
In the given question, the only figure that would be parallel to line c is line d. Line a is not parallel to line c (since it is slightly diagonal, it would intersect line c at a point) and line B is perpendicular to line c (since it is horizontal to plane Q), same as plane Q. So that lines c and d are parallel to each other.
