An electromagnetic wave moving through free space cannot be seen by the human eye. What could be a suitable wavelength for the wave?
- A$4.5 \times 10^{-10}\ \text{km}$
- B$6.2 \times 10^{-7}\ \text{m}$
- C$5.4 \times 10^{-6}\ \text{cm}$
- D$4.2 \times 10^{-4}\ \text{mm}$