18.如右圖所示之 RLC 串聯電路,若已知 v_L(t) = 20cos(100t - 53°) V,請問下列何者正確?(A) = 50∠-90° V(B)= 50∠90° V(C)= 10∠-37° Ω(D) = ∠-53° Ω