A speck of dust is 5.0 x 10-7 m wide. Which of the following is the best way
to rewrite this quantity, using more appropriate units?
A. 5.0 x 10^-7 m
B. 5.0 x 10^-4 mm
C. 5.0 x 10^-5 cm
D. 5.010^-10 km

HELP PLEASE