[问答题]
A 21-speed bicycle has pw,)h5r .nr tfsrti96cvk4wb 6) tts1seven sp6ct 2k8q2 nyiwrockets at the rear wheel and three at the pedal cranks. In which gear is it harder to pedal, a small rear sprocket or kwyqtnc28i2 6a large rear sprocket? Why? In which gear is it harder to pedal, a small front sprocket or a large front sprocket? Why?