Answer:
neutrons should be added with the protons
Line 1: straight horizontal line
Line 2: straight line at a slope
Line 3: exponential growth curve
Line 4: the topmost curve (the one that initially increases but then starts levels out)
The sand provides a rough surface on top of the ice for the cars' tires to grip onto. It provides more friction. Salt melts the ice and often provides more friction (the disadvantage is that it eats concrete!).
