[问答题]
A 21-speed bicycle has seven sprockets at the rear wheel a f vou3:xjkdx h)*4ng+nd three at the023.v2x :vvzgtkad g y pedal cranks. In which gear is it harder to pedal, a small rear sprocket or a large rear sprocketatv2d3vg.0g kzv : y2x? Why? In which gear is it harder to pedal, a small front sprocket or a large front sprocket? Why?