Question 4: Which of the following statements is/are true? (multiple-choice, 15 points) (a) In a three-phase delta connection, the three-phase line currents are balanced and always lagging the corresponding load

currents by 30°. (b) The admittance matrix in a system is a symmetric matrix and the sum of elements in each row of the admittance matrix is always equal to zero. \text { (c) A voltage can be expressed by } v(t)=\sqrt{2} V_{r m s} \cos (\omega t+\delta), \text { where } V_{r m s}=10+j 10 \mathrm{kV} . (d) A power factor angle could be positive or negative.