In the circuit shown in Fig. `6.50`, an idel ammeter and an ideal voltmeter are used. Whan the key is open, the voltmeter reads `1.53 V`. When the key is closed, the ammeter reads `1.0 A` and the voltmeter reads `1.03 V`. The resistance `R` is
A. `0.5 Omega`
B. `1.03 Omega`
C. `1.53 Omega`
D. `1.53 Omega`