In an expression $a \times 10^{b}$:

• A
  $b$ is the order of magnitude for $a \leq 5$.
• B
  $a$ is the order of magnitude for $b \leq 5$.
• C
  $b$ is the order of magnitude for $5 < a \leq 10$.
• D
  $b$ is the order of magnitude for $a \geq 5$.