Exercise 1: sample answer

The pedals drove the front wheel directly, so each turn of the pedals covered one circumference. With no gearing, a bigger wheel meant more distance per turn and so more speed, and makers built the wheel as large as the rider's legs could reach. The cost was safety: the rider sat high over the wheel, with weight forward, so a sudden stop or a pothole threw him over the handlebars (a header) from a great height, and mounting and dismounting were awkward.