Which type of ladder has flat steps, hinged back, self-supporting, and non-adjustable?

 Step Ladders

In general ladders are with inclined or vertical set of steps or rungs between two upright lengths of metal or wood. Ladders used for climbing up and down.

Step ladders :

It is a self supporting portable ladder, most commonly used in industries.  Self-supporting means it does not need any support to lean.  So this ladder can be used any where in the rooms. For example middle of the room  where support is not available. Also this ladder is non-adjustable flat steps and hinged back.  

we need to know the time interval during which the force acts. impulse of force = momentum change

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.