Electromagnetic waves of wavelength $\lambda$ and frequency $f$ travel at speed $c$ in a vacuum. Which statement describes the wavelength and speed of electromagnetic waves of frequency $f/2$?
- Awavelength $\lambda/2$, speed $c/2$
- Bwavelength $\lambda/2$, speed $c$
- Cwavelength $2\lambda$, speed $c$
- Dwavelength $2\lambda$, speed $2c$