Why Was the Actual Measurement of the Cosmic Microwave Background

Why was the actual measurement of the cosmic microwave background so difficult?

A) Earth's atmosphere is almost opaque in the region of the spectrum where this radiation peaks (long-wavelength infrared/short wavelength microwaves) .
B) It was never clear where in the spectrum this radiation would fall.
C) Because the radiation has spread out so much since its origin in the Big Bang, it is extremely faint.
D) The predicted frequency for this radiation was in a range not previously detected, so specialized equipment had to be designed and built.