[问答题]
A 21-speed bicycle has seven sprockets3 kw)bvd/1 a2eafm: jt at the rear wheel and three at the p3gufs;v* wk7 gedal cranks. In which gear is it harder to pedal, a small rear sprocket or a large rear sprocket? Why? In which gear is it harder to pedal, a small front sprocket or a large front sprocket? Whg uwsg7 fkv*3;y?