Which of the following statements are true?
(a)at any junction point in a circuit, the sum of all the currents entering the junction must equal the sum of all the currents leaving the junction.
(b)kirchhoff's junction rule is based on the conservation of energy.
(c)the sum of the changes in potential around any closed loop of a circuit must equal zero.
(d)kirchhoff's loop rule is based on the conservation of charge.