Which of the following statements about the cosmic background radiation is not true?
a) it has a temperature of about 3 degrees k above absolute zero. b) it is the result of a mixture of radiation from many independent sources, such as stars and galaxies. c) it had a much higher temperature in the past. d) it was discovered by penzias and wilson in the early 1960s. e) it appears essentially the same in all directions (it is isotropic)

Microwave background radiation was accidentally discovered by Penzias and Wilson on 1964. This is a form of electromagnetic radiation that is present in the whole universe and completely fills it (it is isotropic).

Its frequency belongs to the microwaves range and is one of the main demonstrations of the of the Big Bang theory model.  

It is important to note the Big Bang occurred 400,000 years before the events related to the microwave cosmic radiation, this means the Big Bang occurred first.