The resistances of a wire at temperatures $t\,^oC$ and $0\,^oC$ are related by:

• A
  $R_t = R_0(1 + \alpha t)$
• B
  $R_t = R_0(1 - \alpha t)$
• C
  $R_t = R_0^2(1 + \alpha t)$
• D
  $R_t = R_0^2(1 - \alpha t)$