An Astronomer Is Observing the Radiation from a Distant Active

Multiple Choice

An astronomer is observing the radiation from a distant active galaxy and notices that the amplitude of the signal varies in strength regularly over a certain period. The maximum possible size for the source of this radiation can now be calculated from the

A) period and the amplitude of the signal.
B) period but not the amplitude of the signal.
C) amplitude but not the period of the signal.
D) frequency of the radiation composing the signal.