A student is studying two electromagnetic waves, X and Y, in a vacuum. Wave X has a wavelength of $5.2 \times 10^{-7}\,\text{m}$. Wave Y has a frequency of $9.4\,\text{GHz}$. Which main regions of the electromagnetic spectrum do waves X and Y belong to?
- AX: radio wave; Y: ultraviolet
- BX: ultraviolet; Y: visible
- CX: visible; Y: microwave
- DX: microwave; Y: radio wave