A.\(u = {u_R} + {u_L} + {u_C}\).
B.\(u = {u_R} + {u_L} - {u_C}\).
C.\(u = \sqrt {{u_R}^2 + {{\left( {{u_L} - {u_C}} \right)}^2}} \).
D.\(u = \sqrt {{u_R}^2 + {{\left( {{u_L} + {u_C}} \right)}^2}} \).