(a) A magnetization B-H curve is divided into three regions: the linear region, the transitionor knee region, and the saturation region. (b) In a magnetic circuit, the total reluctance of

reluctances in series is not equal to their sum. (c) The admittance matrix in a system is a symmetric matrix and the sum of elements in eachrow of the admittance matrix is always equal to zero. \text { (d) A voltage can be expressed by } v(t)=\sqrt{2} V_{\text {rms }} \cos (\omega t+\delta) \text {, where } V_{\text {rms }}=20+j 20 \mathrm{kV} \text {. }