A cell of emf `E` and internal resistance `r` connected in the secondary gets balanced against length `l` of potentiometer wire. If a resistance `R` is connected in parallel with the cell, then the new balancing length for the cell will be
A. `((R)/(R-r))`
B. `((R-r)/(R))`
C. `((R)/(r))`
D. `((R)/(R+r))l`