An iron metal rod is to maintain an accuracy of one part per million. The coefficient of linear expansion of iron is 1 × 10^-5 /°C. The minimum variations in temperature of the rod could be

• A

  $\pm 1^{\circ }\mathrm{C}$

• B

  $\pm 5^{\circ }\mathrm{C}$

• C

  $\pm 0\cdot 1^{\circ }\mathrm{C}$

• D

  $\pm {0.01}^{\circ }\mathrm{C}$