Final answer:
High temperature sources emit electromagnetic waves of high frequency due to the relationship between temperature and wavelength where high temperatures correspond to shorter wavelengths and, as a result, higher frequencies.
Step-by-step explanation:
The relationship f ~ T suggests that as the temperature increases, the emitted electromagnetic waves correspond to shorter wavelengths and higher frequencies. According to physics, specifically the study of blackbody radiation, a hotter source will emit most of its energy at shorter wavelengths; this is evidence that these waves also have higher frequencies.
Considering that E = hf, where E is energy, h is Planck's constant, and f is frequency, shorter wavelengths (and thus higher frequencies) correspond to greater energies. So, when high temperature sources emit electromagnetic radiation, they predominantly do so at higher frequencies. The correct answer to the question is C. high frequency.