f(-x)=f(x)，f(-x+1)=-f(x+1)∴f(-x+1)=f(x-1)=-f(x+1)=-f[(x+2)-1]=-f[-(x+2)+1]=f[(x+2)+1]=f(x+3)即f(x-1)=f(x+3)，f(x)的周期为4,a=f(13/4)=f(-3/4)=f(3/4)b=f(8/3) =f(-4/3)=-f(2/3) c=f(1/2)答案D
