9.一平面简谐波表达式为 =-0.05sin pi (t-2x) (SI单位),则该波的频-|||-率v(Hz)、波速 u(m/s) 及波线上各点振动的振幅A(m)依次为-|||-[ ]-|||-(A)0.5,0.5, -0.05 (B)0.5,1, -0.05-|||-(C)0.5,0.5,0.05 (D)2,2,0.05