Explain the difference between $nm$, $mN$, and $Nm$.

• A
  $nm$ is nanometer, $mN$ is millinewton, $Nm$ is newton-meter.
• B
  $nm$ is newton-meter, $mN$ is nanometer, $Nm$ is millinewton.
• C
  $nm$ is millinewton, $mN$ is newton-meter, $Nm$ is nanometer.
• D
  $nm$ is newton-meter, $mN$ is millinewton, $Nm$ is nanometer.