Answer:
All rungs are perpendicular to a side of a ladder.
Explanation:
The problem tells us that ALL the rungs of a ladder are parallel.
It also tells us that the top rung (which is a subset of all the rungs) is perpendicular to a side of the ladder.
But if this top rung is perpendicular to a side but we know that ALL rungs are parallel, then this top rung is also parallel to the other ones and therefore, all the other rungs are also perpendicular to a side of a ladder.