A.\(H = \dfrac{{{U_N}}}{E}\left( {100\% } \right).\)
B.\(H = \dfrac{{{R_N}}}{{{R_N} + r}}\left( {100\% } \right).\)
C.\(H = \frac{{{A_{ci}}}}{{{A_{{\rm{nguon}}}}}}\left( {100\% } \right).\)
D.\(H = \dfrac{r}{{{R_N} + r}}\left( {100\% } \right).\)

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