The maximum elongation of a steel wire of $1\text{m}$ length if the elastic limit of steel and its Young's modulus, respectively, are $8\times 10^8{\text{N m}}^{-2}$ and $2\times 10^{11}{\text{N m}}^{-2}$ is:

1. A
   $4\text{mm}$
2. B
   $0.4\text{mm}$
3. C
   $40\text{mm}$
4. D
   $8\text{mm}$