Which one of the following expressions gives the potential difference across the third resistor R3 when resistors R1,R2 and R3 are connected in series to a battery of emf V?
a) V3=VR1+R2R3
b) V3=VR3R1+R2
c) V3=VR1+R2+R3R3
d) V3=VR1R2R3