f(x)=πx+log(2)x是(0,+∞)上的单调增函数
f(1/4)=π/4+log(2)(1/4)=π/4-20
f(1/2)=π/2+log(2)(1/2)=π/2-10
∴f(x)在[1/4,1/2]上有零点
选C