[tex]a^{-n}=\dfrac{1}{a^n}\\\\10^{-n}=\dfrac{1}{10^n}=0.\underbrace{000...1}_{n}\\\\\text{examples:}\\\\10^{-2}=\dfrac{1}{10^2}=\dfrac{1}{100}=0.\underbrace{01}_{2} \\10^{-4}=\dfrac{1}{10^4}=\dfrac{1}{10,000}=0.\underbrace{0001}_{4}\\\\\text{therefore}\\\\0.\underbrace{000001}_{6}=10^{-6}\\\\\text{Answer:}\ \boxed{B.\ 10^{-6}}[/tex]
