10-3m
10-6m
10-9m
10-12m
Answer is Wrong!
Answer is Right!
The correct answer is $\boxed{\text{B. }10^{-6}m}$.
A micron is a unit of length equal to one millionth of a meter, or 10 to the minus 6th power of a meter. This is equivalent to one micrometer, or one thousandth of a millimeter.
Option A, $10^{-3}m$, is equal to one millimeter. Option C, $10^{-9}m$, is equal to one nanometer. Option D, $10^{-12}m$, is equal to one picometer.