Two coaxil solenoids 1 and 2 of the same length are set so that one is inside the other. The number of turns per unit length are `n_(1)` and `n_(2)`. The current `i_(1)` and `i_(2)` are flowing in opposite directions. The magnetic field inside the inner coil is zero. This is possible when
A. `i_(1)!=i_(2)` and `n_(1)=n_(2)`
B. `i_(1)=i_(2)` and `n_(1)!=n_(2)`
C. `i_(1)=i_(2)` and `n_(1)=n_(2)`
D. `i_(1)n_(1)=i_(2)n_(2)`
