Acceleration!!!
help

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other

Amicroscope, because these cells are so small that you would not be able to see them, or what they attack without it.

The answer would be d. hope this : ))