At What Temperature Would the Peak Wavelength of Blackbody Radiation

Multiple Choice

At what temperature would the peak wavelength of blackbody radiation correspond to electron-positron pair production? This would have been the lowest temperature in the early universe at which this effect was common.(Note that a photon's energy is equal to , the cosmic background at any point in time has a blackbody spectrum that peaks at a wavelength , and the mass of a single electron or positron is 9.11 *10^-31 kg.)

A) 2400 K
B) 420,000 K
C) 2.4 million K
D) 42 million K
E) 2.4 billion K