The actual yield of a reaction can be compared with the maximum theoretical yield to calculate what?

Rain is pulled by gravity which is a non contact force

If its history of, then b) because a) implies only present day (now)

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

Answerthe distance between the two ends of the galaxy is 150,000 light years;