The length of a metal wire is l₁ when the tension in it is T₁ and is l₂ when the tension is T₂. Then natural length of the wire is
A l₁ +l₂/2
B √(l₁l₂)
C l₁ T₂ − l₂T₁ / T₂ −T₁
D l₁ T₂ + l₂T₁ / T₁ + T₂