The length of a steel wire is `l_(1)` when the stretching force is `T_(1)` and `l_(2)` when the stretching force is `T_(2)`. The natural length of the wire is
A. `(l_(1)T_(1)+l_(2)T_(2))/(T_(1)+T_(2))`
B. `(l_(2)T_(1)-l_(1)T_(2))/(T_(1)-T_(2))`
C. `(l_(2)T_(1)+l_(1)T_(2))/(T_(1)+T_(2))`
D. `(l_(1)T_(1)-L_(2)T_(2))/(T_(1)-T_(2))`