The frequency of light ray having the wavelength 3000 Å is

• A

  $9\times {10}^{13}\text{ cycles/sec }$

• B

  ${10}^{15}\text{ cycles }/\text{ sec }$

• C

  $90 \mathrm{cycles}/\sec$

• D

  $3000 \mathrm{cycles}/\sec$