c.降低了4%；结果与原价相比=1-[(1+20%)*(1-20%)]*100%=4%
1×(1+20%)×(1-20%)=0.96降低了4%满意请采纳
c.降低了4%；结果与原价相比=1-[(1+20%)*(1-20%)]*100%=4%求采纳
