In an ideal transformer, number of turns in the primary and secondary are `N_1` and `N_2`, current and power in the input and output are `I_1,I_2`and `P_1,P_2` respectively. Then
A. `I_2=I_1N_1/N_2`
B. `I_2=I_1.N_2/N_1`
C. `P_2=P_1`
D. `P_2=P_1N_1/N_2`