Hysteresis loops for two magnetic materials $A$  and $B$ are given below:

These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use:

The $B-H$ curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with $1000 \mathrm{turns} {\mathrm{cm}}^{-1}$. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is, 

A capacitor of capacitance $C$ is connected to two voltmeters $A$ and $B$ (figure). $A$ is ideal, having infinite resistance, while $B$ has resistance $R$. The capacitor is charged and then the switch $S$ is closed. The readings of $A$ and $B$ will be same.

In the circuit shown in the figure, an ideal ammeter and an ideal voltmeter are used. When the key is open, the voltmeter reads $1.53 \mathrm{V}$. When the key is closed, the ammeter reads $1.0 \mathrm{A}$ and the voltmeter reads $1.03 \mathrm{V}$. The resistance $R$ is