Exercise 2: sample answer

Tension-spoked wire wheels: thin spokes pulled tight make a wheel that is light and strong, so large wheels became practical, and the same construction is still used on bicycles today (check who developed it). Hollow steel tubing for the frame gave strength with low weight, and is the basis of most frames until modern materials arrived. Ball bearings in hubs and pedals, also from this period (check), reduced friction. Any two of these, with the reason they mattered, is a good answer.