Answer:
D. Using the top ladder as a step
Step-by-step explanation:
You are given suggestions for use of a ladder, and asked to identify one that is unsafe.
Ladder safety
In general, you will want to make sure a ladder is locked so that movable parts cannot move, and placed on a stable, level surface at an appropriate angle. It can be helpful to have someone hold the ladder for you to make sure it does not move. It is always a good idea to face the ladder while climbing up and down, so that you can appropriately grip the rails.
The one practice listed here that is unsafe is using the top step of the ladder.